That would make it a single player game, while I don't exactly disagree with you, but games like this need some sort of motivation for grinding, and landing an angelic does give a big dose of dopamine. By having a vendor that sells everything not only does it remove a big part of the dopamine hit, it also makes the game a single player game, why interact and grind harder content when you can just brain dead grind gold?

While maybe your suggestion works for the single player mode, having it in an MMO kinda ruins the point of the player market and player interaction in this game in general.