So right now I'm playing in a game where we're tackling a very large dungeon (Scarlet Citadel by Kobold Press). The first few sessions was about saving up money to get full plate for the Cleric. Then we had a small tangent about buying a cart and paying for rooms at the inn for a week in advance, followed by "where are we going to get healing potions, anyways?".
We're now level 6, and the only pressing use for gold is helping my Wizard add key spells to their book and paying for a few costly components (like the holy water needed for Protection from Evil/Good, which was absolutely vital in one encounter).
The DM keeps telling us that magic items can be sold in the major city, but enough stuff is happening locally that any such side trek would likely have dire consequences. We have a pile of treasure we can't even liquidate in town, and we've already basically warped the local economy around our party to the point that I think our leaving will cause a recession!
Not that we haven't attempted to invest in the town; I'm wooing two merchants who can provide low key magical goods, but I'm purchasing said goods faster than they can make them. The only reason I don't have a pile of scrolls is that I don't think taking a few days off when there are active factions of people up to no good in the lower levels of the ruins.
So it's an interesting situation where it's not so much that we don't have the ability to spend money on anything, as we simply don't have the time to do so, so it's been collecting in our coffers (my share being much lower since I try not to burden the party with my spell scribing fees- even if I'm starting to really resent the Cleric, who can pray for all kinds of 3PP spells on a whim, while I have to find everything and pay for the right to use it).
Now some might say "oh you're getting too much gold", but honestly, this feels about right compared to my AL experience. Just in AL, spending money on anything more than healing potions and spellcasting services is a real hassle, so it's no big deal for a character entering Tier 3 to have 10k gold laying around.
So bottom line, in answering the question posted in the OP;
No, there's no real purpose for the classic "Imma gonna rob the countryside of anything not nailed down" character, let alone a Rogue by default. The PHB is mostly full of "level 1-3" purchases, and even enforcing trivial things like rations, ammunition, and lifestyle fees isn't going to matter by level 5-6.
The DM has to, in my opinion, present some of the following sorts of things to the campaign:
1) reduce the wealth of characters. Not a fan of this one, as adventuring ought to be a lucrative enterprise. The fact that a Tier 2-3 adventurer could just buy an inn and retire can be problematic if your character has no goals other than "get rich" leads into my next point.
2) every character should be made with a long term goal. Restoring your family name, investing in a side enterprise, rebuilding your home town; every PC should have a long term goal that involves them funneling some of their cash to achieve it. Clerics should definitely be tithing to their deity, for example. I can only imagine the demands a Patron could make on a Warlock; enterprising Fiend Patrons could easily have a "buyback" price set for the Warlock's soul, if they can manage to save up enough money! The fact that so many games have characters with sketchy backgrounds that basically come down to "yeah so I want to play this character with this group of weirdoes and not really stretch my brain to think of anything deeper" is a big contributor to the gold problem (where it exists). However,
3) gold funnels should be investments, not taxes. I've played under a lot of DM's over the years who are happy to let players spend money to buy a base of operations only to send them on a grand tour of the cosmos. Or let the players invest in a town/church/orphanage/whatever just to take money off their hands.
The DM should always be working to make the players feel like these investments matter. Whether they are earning the favor of a divine, a particular faction, or even a worthy patron (lower case patron), investments now should lead to rewards (and interesting opportunities later). A lot of DM's have this idea for a few adventures and don't really plan ahead for a living campaign- in games like this, money piles up quickly because nobody feels like the setting is "real"; it's a facade, a backdrop of nameless NPC's and token descriptions placed over a small menu of options like, "buy PHB equipment here, quest location there, notable NPC here, possible magic item vendor there".
I've often pitched to other DM's the idea of giving the party a patron who represents a guild or other faction, that can offer the players all the services they need, as well as a source of ongoing missions, where the players can earn "pull" by not only going on adventures, but investing in the faction itself, sort of like being paid in stock options that can pay off in dividends later. Unfortunately, this usually doesn't get anywhere, because of my next point.
4) don't be afraid of magic items! So many DM's balk at the idea of players actually purchasing magic items that they want to have. Even in editions where this is the norm, I've had DM's act terrified that a player will find that one item that will totally break the game wide open as they get too much of something- be it damage, accuracy, AC, what have you.
In 5e, this is especially ludicrous, as the abilities one gets from class and race are (with a few exceptions) really tame. Bounded accuracy means a +1 to hit or damage means you "win more" against things you're supposed to beat, and gives you a slightly better chance to deal with things you're not supposed to beat. How many adventures pit players against Deadly+ encounters, or have them face things far above them in challenge?
Playing Storm King's Thunder, I saw Tier 3 characters dealing with CR 17+ foes and eking out victories- you can't really tell me a flametongue sword or a cloak of displacement is going to make that much of a difference.
Now I'm not saying "oh yes, offer Very Rare and Legendary items wholesale", but if you're using magic items, you're probably using attunement, which really puts a damper on how much cool stuff someone can even use to begin with. And there's lots of magic items that aren't even going to matter much in combat, but give characters the kinds of non-combat options that normally only come with the use of spell slots! I had an occasion to acquire a Robe of Eyes in AL, and my character used it to foil an ambush and find a hidden treasure they normally wouldn't have.
The DM griped about this, saying it trivialized the adventure, but we still had to fight the Duergar assassins, I just noticed them sneaking up on us. And as for the invisible treasure chest, why is it even there if players aren't meant to find it?
I get some people like their low powered games, but D&D is at some point supposed to transform into more heroic, and even superheroic play at higher levels. Acquiring epic swag to give you the tools to deal with higher level adventuring (and as rewards for same) is part of the game's legacy, and can be a lot of fun.
And there's other kinds of rewards that aren't physical items as well. Boons, grandmaster training, bonus feats, a chance to raise an ability score beyond ASI's- the sky is really the limit, if you're not constantly worried that the players are going to actually win; too many people focus on the fact that it's difficult to make D&D characters lose, without realizing that's kind of a feature, not a bug. I personally have found that it's hard to have a long-running campaign for people to get invested in if their characters are always dying off and never succeeding! This doesn't mean that the meatgrinder low fantasy "bring 10 character sheets to a session" style of play can't be fun for some, but it's a very different experience than what the game has been about for some time (unless you're playing in a Ravenloft game, of course).
So if you want players to invest in purchasing their own ship, acquiring status with nobles, building a fortress with teleportation circles, or even funding other adventurers, the DM does, unfortunately, have to help the players come to the realization that these are actual options, and not just ways to make excess gold vanish without a trace. And you know, some groups don't care about this stuff, which is unfortunate, but I think that's something you need to sit down with your group and discuss.
What role do they want loot to portray in the game? If they just want a beer and pretzels dungeon crawl simulator with no real story, then sure, let them have mountains of gold, let them all be kings, and hock their crowns between sessions paying for epic orgies or whatnot.
But it's equally possible that you can help your players see that wealth is another way to engage with the setting, and really immerse themselves in the fantasy world being presented.
Now, should this sort of thing be more integrated into the game already? With the DMG giving out deep, meaningful guidance to new DM's about this sort of thing? Absolutely. It's a crime that it isn't, honestly, because it cheapens the experience for people who have never had the chance to engage with a game world on a deeper level than "here's this place where the adventures happen". There's not much we can do about that though; at some point, if you want your campaign to be more than a facade, you need to roll up your sleeves and get to work.
Just make sure that your group is on board; if all they want is an MMO without a 15 dollar monthly subscription, that's unfortunate, but understandable. Sometimes after a rough week of adulting, you just want to play Raff, Son of Ulfric, Slayer of Minotaurs and throw dice and deal some damage and not worry about whether the merchant consortium you've invested in should acquire spices from Calimshan or werewolf pelts from the Moonshaes.
