People can and did amass this kind of gold without leaving a major city after a time, simply by playing the AH. Prices are up in general because people know how to play the AH better, and gold flows a lot more freely between known farming locations and dedicated strategies.
You could nerf all of the high level dungeon farming methods with some extreme absurdities and people would still find a way to cap out gold/hour using lower instances or outdoor areas. Are you seriously going to demand that SM:Cath be changed in some material way to prevent lvl60 Mages from one-pulling the whole place and AoEing it down? Someone may find a way to generate 30 g/hr doing some shenanigans in Gnomer! Better fix it quick!!
Meanwhile Rogues can run laps using pickpocket in BRD to score a decent hunk of change and items. Shall we give everyone stealth detection? Maybe eliminate the pocket change from murdering Humanoid NPCs?
Part of the “warts and all” facet of Vanilla is that a lot of instances were neat to look at, fun to walk through, and horrendously tuned to eliminate every form of wacky behavior. Each expansion since then has taken efforts to minimize this like reducing dungeons down to essentially long hallways with no looping, narrow passages with stealth detection, and terrain geometry that any NPC can traverse.
All of this being said, the biggest gold sink right now is Black Lotus, which is ludicrously high not because of any industrious Hunter, Mage, or Warlock… but because they only spawn in the world at a limited and set rate. Because of the solo farmers, even right now while Lionheart Helms are still being made like crazy and folks are saving up for their Thunderfury, Arcane Crystals aren’t overpriced compared to early Vanilla AH prices. As time goes on and phases release, these will drop in value similar to Devilsaur Leather.
Black Lotus on the other hand has no way to scale up the acquisition to accommodate the population. Open world farming is too much for average Joe’s like myself, so we instance farm and can do so reasonably well. DM, ZF, Mara, SM, and others are relief valves to handle the fact that even with higher node spawn rate, the population out and about is just too much. We have no such relief valve with Black Lotus.
Gold farming is NEVER GOING AWAY. You want a more authentic Vanilla Market? The only real absurdity is Black Lotus due to massive populations. Address that, not the Warlock using Enslave Demon and terrain pathing to have some fun in Dire Maul.