Well, I know that I never seem to have enough money to buy and scribe all the spells I want. A proper wizard learns every spell he possible can. And keeps a backup spellbook.
Expensive components can add a reasonable cost too. Not just the consumed ones (though that can end up being one of the biggest expenses), but initially buying the reusable components. My 5th-level cleric spent almost all his money making sure he could cast every spell he had access to at least once. I didn't want to end up planning to prepare a different situational spell the next day, only to realize I don't have a costly component for it.
Also, while it shouldn't be an issue after low-level, the cost of living is a thing, and you should either be paying upkeep, or specifically paying for food and lodging.
I don't know if DMs are just skipping those costs, but if you are letting your party cast free revivify and never pay for food, well, that's not the game's fault. It has listed costs for those things for a reason.
That issue out of the way, assuming your group isn't just handwaving all the actual expenses the game includes, you move into more subjective playstyle territory.
My characters like nice stuff. They aren't just a block of statistics made to kill monsters. They are an imaginary person who decides to keep some of the jewelry and art objects they find because they like them. Even though we do have actual places you can buy magic items (nothing like 3e, and significantly more expensive than the cheap (and seemingly cheaper and cheaper as the product line progressed) 5e prices), those are competing with the other things we want. Vehicles, mounts. A fancy set of clothes or accessories. I had the hide of a young black dragon we slew turned into armor. No statistical benefit over non-magical armor, but it sure makes a statement and costs a lot more. Found a dwarven smith so I could make sure to get the quality work I wanted. We also got daggers made from teeth.
I mean, am I the only one who built and decked out all the manors in Skyrim's expansion? I do the same sorts of thing in D&D. Are there a lot of players who do that sort of thing in video games but don't in D&D? I find it at least as satisfying in D&D. Is it the fact that you don't get the built-in visuals provided, and you have to either find/make art or keep it in your imagination? Works for me. I regularly imagine that dragon armor with it glossy black scales, gold trim and red gemstones. My character might even not wear it when they want to avoid standing out so much.
When people talk about not having anything to spend money on, I just wonder how their games play, because I don't expect I'll ever run out of things to spend my imaginary money on in a game where I'm imagining living in a fantasy world.
I suppose if your games are only about battles and adventures and you completely gloss over or aren't interested in anything between, and don't like to imagine what things look like, and don't have any players who like to make art for their characters or the party, and let people cast expensive spells for free, and just convert all your treasure into coins rather than admiring it, then yeah, you'll probably find your money just turning into an ever increasing number on your sheet. It just feels to me like choosing to combine not following some of the game rules with not engaging with the role-playing immersion the money is mostly there for, and then wondering why it's there. And that's fine, but that is why it's there.
Am I missing something obvious?