[MichaelGG]

Probably because there's a small market for that? I've met technical people that don't even make their CSRs, they actually have their CA generate private+public keypair so they don't have to figure it out.

Also, CAs make more money if they can issue each leaf cert themselves. Some CAs don't even allow you to get multiple private keys signed (only one active at a time) without paying more.