As it was pointed out the living costs are very low compared to the money adventurers make. There is hardly any equipment to buy especially now with magic stores having closed and even consumables are not really tracked in 5E.
Sure you can use money as bribes, but as D&D is mainly a dungeon crawler they come up only sporadically and because NPCs dont make much money they too have hardly an impact on the PCs wallet.
Sure you can spend money during downtime, but why have downtime in the first place? Healing is pretty much instant and there is no need to stop adventuring. The published modules certainly dont see a need for extended downtimes.
Also the adventuring lifestyle actively disincentives owning property as you will be on the road most of the time anyway. So even if you buy a castle the only thing that changes is that instead of a large sum of money you have castle written on your character sheet with no effect.
Compare that for example to Shadowrun. You have to buy better equipment, consumables, have to replace equipment in case it gets damaged or you had to ditch it which can get very expensive in case of drones and cars and lifestyles are not only expensive, you might even want to maintain severals as hideouts. And because of the healing rate in SR you will likely have more downtime than in D&D. And lastly there are a lot more opportunities for bribes or paying others to dig up stuff.
Shadowrun and many other RPGs have been designed around money being a ressource and used for advancement. D&D has not. Money is just a score you can look at to feel accomplished but which has no impact on the game.