Casters often feel at a massive disadvantage for casual fights. For a boss fight, casters are often the strongest, since you'll blow all your spell slots. But for smaller fights, you want to preserve your spell slots and cantrips simply cannot keep up with martials. I mean, a single attack roll for a spell cantrip vs getting 2-3 attack roles that also do more damage total? Heck, my strongest martials can usually do at least double the damage of a spell caster's cantrips.
Though at the same time, when I can blow the spell slot, no martial can outdo the AoE damage of reliable ol' fireball or the likes. Just I can't justify using my spell slots on a small number of weak enemies.
While I think the rich are one of the most influential sources of it, I'm not convinced they're the only or even the majority. Like, of the rich stopped using bigotry to divide people, would people stop being bigoted? I don't think so at all. I think there's something wrong with humanity that makes it easy for bigotry to evolve even in the absence of power and perhaps worse, for people to want to be bigoted.