We are a furry art archival, and want predominantly furry art. We also accept things that don't have fur when they're fantastical enough to still be somewhat relevant.
We don't accept pure human art because it would absolutely eclipse the furry art we actually want. Furry is a niche, gelbooru has 4.3 million posts, we are still sitting well below 2 million.

It would definitely not be convenient to us to suddenly have even more things that need to be curated and maintained. Even if something has been accepted the work doesn't end there.