Do the founders you know personally come from wealthy backgrounds?

No, unless by "wealthy" you mean that the average student at Stanford/Berkeley/MIT doesn't come from a poor family.

My experience is primarily with Palantir. Almost all the founders I know worked together at Palantir, went into business to work on problems they first encountered at Palantir, got angel investment from wealthy early Palantir employees, and got connected to institutional funding through those wealthy Palantir investors.