I don't think that (despite the efforts of animal support/tech groups to capitalize on some animals being able to paint^[1], sculpt, or dance^[2]) most serious art aficionados don't believe that animals are actually able to create art even if they are doing it with all their hearts and souls. It may be that art is a function of human intelligence as much as creativity is a function of art, as determined by those who decide what is "art".
With that in mind... perhaps non-humans can't create art simply because they aren't human.

1. Speaking of Congo, a lab chimp:

While he never painted identifiable images – no portraits, no landscapes, no still lifes – Congo's style was unironically described by some as "lyrical abstract impressionism". He seemed to have a sense of intention in his paintings, and a sense of coherence. If his paintings or brushes were taken away before he felt he was done, he whined until they were returned to him. If he had completed his work, he refused to continue painting even at Morris's prompting.

2. Dance in this article relies on the ability to co-ordinate movements with music