There is probably a doctoral thesis in this somewhere.

Cartoons had a wealth of both animal and human characters. Betty Boop cartoons had both. So do a lot of others. Many Warner Brother's cartoons featured humans, but, when I think about it, usually as villains or fall guys. Almost all were white.

Disney's famous features often featured human characters, but in "dramatic" more than comedy roles.

I suspect animals were indeed more appealing, and more importantly, they could pull stuff that would look a bit twisted if a human was doing it.

Carl Barks had human characters in his duck comics, but he stubbornly gave them floppy ears and "dog noses."

It would be fun to read a detailed analysis of this kind of thing.

Three-fingered hands just made it easier to animate. Same reason Harryhausen's giant octopus had only five tentacles.