I can't remember which "running the game" episodes I saw them in, but I felt Matt Colville did a good job articulating some of my sentiments as far as Treasure and things go. I'll put them down as briefly as I can here.
Early editions of D&D (and AD&D) presupposed the goal of adventuring was to "get loot" (treasure and magic items) - to the point where 1 gp looted = 1 XP. It also presupposed that the characters would have something they wanted to spend that loot on - i.e., that your motivation for going into a dungeon was not "save the princess" or "protect the townsfolk" but because "it's socially acceptable to kill the denizens and take their stuff."
The original game did not give much in the way of bonuses for exceptional stats; your survivability was almost entirely based upon your gear at lower levels (remember, you didn't get a Dex bonus to Armor Class unless your Dex was 15+ and you didn't get a strength bonus to hit unless your Str was 17+ in AD&D, and in D&D 13-15 gave you a +1, 16-17 gave you a +2, and only an 18 gave you +3), so saving up enough to get your fighter or paladin into plate mail was important! Games were more meat-grindery so much so that the "4 person party" assumed in later editions wasn't so much a thing - you expected 6 to 10 characters plus hirelings, plus henchmen, plus followers, etc. - but the game was MUCH bigger on activities to do in downtime (strongholds, businesses, hiring sages to research stuff, etc.). Ability score boosts due to magic items were incredibly rare (usually one-time boosts of one point, such as a Manual of Health or similar) though dungeon features that randomly changed your attributes were thicker on the ground (drink from a pool, roll d%, oh, hey, you get a +1 to Strength... oh, hey, you die instantly and turn to stone).
Third edition was kind of an odd duck in that it was the first one I can remember that built into the character curve the assumption that characters would have a certain amount of magical kit at specific levels, that they got ability score increases (including increases from items), and generally made available a lot of feats that granted bonuses that improved survivability immensely. In addition, previously lackluster ability scores now granted significant bonuses - and with the assumption your ability scores were going to increase, you would get even bigger bonuses! This helped a lot with designing adventures that could challenge PCs of a particular level because you knew what the combat math was going to look like, but you now depended much less on your Gear and much more on your Feats. Also, because your character started out at a much higher power level than previous editions, gained power much more quickly, and you could reasonably assume the DM would be giving you the appropriate gear to help you improve - he was specifically told to by the DMG! - there was much less urgency to get hirelings to act as cannon fodder, to accumulate gold to kit yourself out, and so forth. Rules for strongholds and dominion ruling - which I never felt were emphasized in AD&D (they were rather emphasized in D&D, particularly in the Companion Set) - weren't stressed in 3E either. The only thing Gold was useful for was as currency to buy the magic items you want and it was explicitly part of the game that the two should be relatively easily interchangeable. Playing a character that was much more powerful (at the same level) than before, and for whom the DMG itself provided for showering with exactly the right amount of magical gear to power you up in all the ways that mattered, that reduced the need for treasure. And of course, in 3E, XP was decoupled from Gold Pieces, as the implicit assumption was that the fun part of the game was "overcoming challenges" (combat, skill challenges like traps or social setting obstacles, etc.) and that the characters had no intrinsic drive to accumulate wealth (why would they need that drive? The DMG explicitly stated how much to give them! Enterprising players couldn't get ahead of the wealth curve for their level and lazy players couldn't get behind the curve). Also, the "Downtime" game mode was not really supported at all outside of "Craft Magic Item" Feats (and since those just rolled back into the "combat" system for the most part, I don't count those). The tactical combat side of the game was supported more robustly than ever, but at the expense of "Exploration" and especially "Downtime."
4th Edition moved almost everything into class abilities (feats) and out of gear, even further reducing the need to accumulate wealth. Downtime and, to a lesser extent, exploration mode continued to be de-emphasized in favor of tactical combat.
5th Edition did take a little emphasis off class abilities and put it back on gear, but since the XP system didn't go back to awarding characters for plunder, it's clear the assumption is still that the DM will feed players treasure at the appropriate rate for their level and that lazy characters will still be taken care of and enterprising characters still won't be able to get significantly ahead of curve. There has been a little more lip service given to the "Exploration" mode, but "Combat Mode" still dominates and "Downtime" mode is notably absent.
Note Pathfinder (1E and 2E) also explicitly state characters of Level X should have Y levels of magic and wealth. They also explictly describe the "Encounter" and "Exploration" and "Downtime" game modes but I still haven't seen a ton of support for the "Downtime" game mode.
It is here where I think BECMI did the best job of any edition in really supporting varied Downtime activities - in the Basic rules, players go shopping for gear between adventures, once they can afford the best gear, players are explicitly encouraged to settle down and build (expensive!) residences in the Expert Set - around "Name" (9th) level and rules for building Strongholds are given there, the Companion Set introduces ruling a domain and the expenses that go into that (including maintaining armies), and the Master Set sinks resources not only into running your nation, but into sacrificing stuff for an audience with the immortals and obtaining artifacts. It suffers from not having strong magic item creation rules like 3E did (like them or not, they are at least the most comprehensive set of rules in the core rules of the various editions).
So where does that leave us? It leaves us in a situation where there's no in-game incentive for characters to desire to accumulate wealth and magic items. It's more balanced in the tactical games, and thus encounter math works better and it's easier to design encounters - all of these things make the DMs life easier in combat - but it means that while actually gameplay is focused around combat - "Kill the Monsters" - the second half of that, "Take Their Treasure" has been largely removed from the game. More importantly, the "Downtime" mode - where most of the Treasure that comes in during "Encounter" and "Exploration" mode is siphoned off - with no place for that to go, it just keeps accumulating. It's why treasure seems to have no value in 5E - once you kit up at level 2 or 3 you've really got nothing to spend it on going forward and unless you are an old-school gamer whose character is likely to have come to the table with plans on how he's going to spend the outrageous fortune he makes adventuring, you aren't going to know what to do with it because including in your backstory "what would you do with a million gold pieces? No really, you need an answer for this" just isn't a thing any more.
