As someone who works in the art industry, I can say that this is really not the case for the majority of artists, gallerists, and collectors. A lot of people working in this industry, especially outside the major centers of wealth (New York, London, LA, etc.) are really just making fairly unremarkable middle-class incomes, and do it because they like art and genuinely believe in its cultural importance.

That might not be the case if you're looking at the Saatchi collection or wandering about in one of Larry Gagosian's spaces, but they are the wild exception to the rule.

While his art isn't in galleries, Banksy can certainly count himself among the wealthiest of artists, despite his anti-capitalistic nature, he's still raking in millions from his works.