You're basically stealing shit to sell.
Because money is so great in a world where there isn't anything of worth to buy.
This is a problem with a lot of games, maybe even most. Most modern RPGs, whether open world or not, are horrible at creating balanced, playable economies. FO:NV was better than most, but even still, by the end of the game you are fucking swimming in money and there is nothing left to spend it on. To see really well balanced economies I feel like I have to go back to really old games like Betrayal at Krondor and the Quest for Glory series. In Bethesda games, money eventually becomes just another collectible.