why does that matter? because for 10,000-15,000 gp in AD&D, you could buy
Nothing. You couldn't buy magic in AD&D. The GP amounts were there for XP rewards you gained for creating the object, and for the sale price. It was explicitly
not the price the players could buy the item for. Prior to 3e, magic items were not available for sale as a general rule. In 1e, gp could still be counted for XP (at least for some classes, I'm sure), but that rule became entirely optional in 2e. All you can do with money is build a fortress/tower/etc., live well, and do spell research. In 2e, you can give the PCs 50 million in gp, and there's often very little they can do with it, practically speaking.
In 3e, 4e, and PF, you can dump money into magic items, either buying them or creating them. Gold = magic in those editions, and so gold becomes much more valuable to PCs. You find 5 million in gp, let alone 50 million in gp, and you're decked out like epic level characters.
In 5e, as a general rule the only magic items you can buy are
potions of healing for 50gp each. You're back to gold not being able to do very much for PC power. Once you've got a full set of weapons, full plate, a shield, and whatever kits and tools and animals you want, you're done. Unless you're a Wizard, no PC needs more than about 10,000 gp in wealth, barring material components. There's really very little to spend money on beyond that to increase your individual power. If you're a Wizard, you need about 50,000 gp and about 8 months to copy every spell in the game into a spellbook (less whatever spells are learned at level-up). So what good is finding 50 million in gp? It's just money.
Now, sure, you buy land and ships and horses and castles and armies and towns and temples and fortresses and more land and more armies and allies and mercenaries and more land and bigger ships and so forth. Money is still powerful, but it's not liquid like it is in 3e-4e. It can't be directly invested into individual combat prowess like in 3e-4e. It's not nearly as good for being an adventurer. You can't rank up to S+ just because you've got the money to do it. You can't leverage wealth to concentrate power into your character like magic does.