Furry fandom meets markets which are not well-served by the organized corporate world - and custom cartoon porn is probably the largest of them. That doesn't mean fans don't like other anthropomorphic things, just that it's what makes artists money (and some like drawing it as well), so they make more of it.
Other under-served markets include serious works about what it would be like if intelligent anthropomorphic animals existed, and custom animal costumes.
Furry fandom meets markets which are not well-served by the organized corporate world - and custom cartoon porn is probably the largest of them. That doesn't mean fans don't like other anthropomorphic things, just that it's what makes artists money (and some like drawing it as well), so they make more of it.
Other under-served markets include serious works about what it would be like if intelligent anthropomorphic animals existed, and custom animal costumes.