It's mainly because those artists and creators have far less hangups about what they're doing and generally ignore detractors.
The fact that they usually even shrug off their own personal interests for people willing to pay means they get more commissions at a more consistent rate, meaning more practice and lower fuckup rate with a much higher rate of productivity.
So far as I know, the only known non-fur artist in these circles that seems to have this realized is Nitrotitan/Modeseven. He probably has raw caffeine for blood and modybuilder sculpted arms by this point at his present output rate.
I still remember when he started and had a more blocky and adorably amatuer-ish style, but he's basically refused to stop over the course of all these years and practically shat on every other artist in any field in terms of consistent productivity while leaving no kink or fetish unexplored by personal views and now he's Faptain of the 69'th division while everybody else is just an insecure private.
I'm not sure what he's doing with whatever money he gets because it certainly doesn't seem like he's using any time at all to enjoy or spend it.