When I first started my GURPS DF game, the amount of treasure was an issue. That wasn't enough. I was putting in too little and ensuring a steady stream outgoing.
I made a mistake in too-closely following the amounts of money found in B2 The Keep on the Borderlands and just updating them to GURPS - silver to $0.10 coppers, gold to $1 silvers, platinum to $100 gold coins, etc. I'd eventually sort out the steady stream outgoing - upkeep went from "per real world week between sessions" to "once between sessions." But the incoming was still a a bit sparse.
My megadungeon had the same issue at first, but I cleaned that up as I went, going back through it and adding in extra treasure. Even so, I learned a few lessions.
You can't assume the same PCs will get the money.
PCs might die. People might switch PCs. New players might show up, forcing an additional split on the loot. The PCs might find a great weapon, sell it for 40% of its value, and then someone comes along who can use that weapon - and then buys a new one of the same kind at 100% value. PCs might sell useful gear now because it isn't seen as useful then buy the same gear later. A player might run a PC for a while, accumulate a lot of loot, and then stop playing because real life impinges on the game schedule.
In other words, the total might be divided among more parts than you expected.
You can't assume the PCs will recognize when things have gone dry.
Sometimes the players find a good haul of loot or two, and then leave the area. More often, especially in a repeatedly delved dungeon, they'll end up in the same places repeatedly. They might expect they found only part of the loot and look for the rest. They might clean a place out entirely but think "those guys must have had more money." They might be right, but not recognize they're in the wrong place looking for a stash that is elsewhere.
You can't assume the players will take the risks needed to realize all of the treasure.
Loot might be there, but require a bold move to get it. Especially if the treasure isn't permanently in the location. The Cold Fens was a good example of this in my game. Cognizant of the need for more fungible loot, I put in some. It wasn't scattered around willy-nilly, but it was there. But instead of the PCs steamrolling the fodder-level bandits, they ground them down in a series of drawn-out fights. They'd show up, grind down some foes, then leave.
Each trip cost money, and each trip got a little bit of loot. But the final trip broke the back of the bandits without finding their loot or killing their leader. Their leader took his loot and left. It simply wasn't there any more - too much time spent, some willingly and some not, meant the opportunity was lost.
You can't assume the PCs will save for emergencies.
Just a simple fact - the PCs may have backup money to replace armor lost to rust monsters, weapons shattered by the swordbreaker demon, resurrect the fallen and remove horrible curses.
Or they might have spent it all on potions, scrolls, buying that magic item they desperately wanted, used to upgrade a bow or power item, etc.
You can can't know for sure.
In short, the PCs might not find everything, seize the chances for everything, or have the number of people you expect. You can put in a larger amount of loot to deal with that, but ultimately, they'll control where the loot goes and what it does. And they might blow the money on things and have not enough for dealing with problems that crop up.
My solution to this is larger hauls, lots of things to spend money on, reasonable warning about the need to keep a reserve . . . and a lot of just seeing what happens. I try not to reward caution in a game of paper men taking imaginary risks, and try to reward the things I like - delving deeper and taking risks. But you can't assume the PCs will necessarily do that, either . . .