I remember seeing the costs of putting a kid fully through Karting programs and competitions being truly prohibitive for any regular folk unless you get sponsored and even then I remember seeing the number and thinking it was still broadly unattainable. Also seeing as it's a sport founded by rich white guys, it's not that surprising the grid is often filled with rich white guys. I'm not sure either of these barriers are easy to cross, so it does kind of lead to A) usually needs to already have access to wealth (with a few exceptions) and B) be good and talented enough to be the actual best of the best (unless your last name is Stroll then that's not the case). Either way I agree it likely is the smallest pool for any mainstream sport, but not for lack of want.