This is true, that there was a bit more wiggle room for non-‘traditional’ artists in the past. It’s still true to some degree, artists like Cliff Chiang and Travel Forman do wonderful work and have good followings.
Again, the tendency is to blame this on mean publishers. But if readers are buying mainly slick/scratchy stuff, those are the books that sell and that becomes the message.
I have tried to get some of my favorite eclectic artists on books in the past, it’s hard to make happen, sadly.