Because my favorite thing about RPGs, going all the way back to D&D, is to find 'treasure'. Whether it's a pile of gold, or a deck of many things, or a longsword +1, +3 vs Lycanthropes. I love finding some cool new thing I can use, or trying to hoard up enough money to buy some cool new thing, or buy the materials to get some cool new thing. BUT, if you hit level 25 and have more gold than you could possibly spend, there's nothing to look forward to. There's no new piece of treasure that's going to be exciting.
How does having gold prevent you from finding new exciting items in a dungeon, or new exciting items in a shop? If it's really an issue, you don't have to collect everything from a dungeon and sell it all. If you're looking to roleplay anyway, it's not realistic for you to have the kind of carrying capacity they give you. Force yourself to only pick up a few rare treasures to sell or use and suddenly you'll have a lot less gold kicking about.
This to me is the same as people who complain about the game being too easy or a spec being too powerful because they went ahead and maxed out smithing, enchanting and the melee weapon perks and one-shot everything. The game didn't force you to do that, you chose to do it yourself.