There is a key difference in the way these models are trained - Chess and Go have clearly defined win conditions, so a model can be taught to explore the possibility space and try to reach victory by any means necessary, potentially with strategies which have never been seen before. With art on the other hand there is no objective measure of quality, so the models are instead taught to treat already existing art as the benchmark to strive towards, making them trite by nature.

As I see it AI can absolutely find innovative solutions, but only if you can clearly and explicitly define the problem it needs to solve.