I definitely doubt the average comic author is pro billionaire. I think having an absurdly rich protagonist is just interesting for plot, not just does it easily justify the funding, but it easily generates a lot of plot hooks.

Growing up, I absolutely loved Peter Parker as just being the average broke kid, but I was never excited by the plot that generated that was largely school drama or conversations in small apartments.

On the other hand, there are plenty of cool things that Bruce Wayne gets to do. Sometimes he blends in with high society functions and you get an almost James Bond style investigation and sometimes you capture that Dracula style recluse skulking in his enormous manor, and both of those are very evocative even before you consider how it funds his heroics.