If some don't understand why, I argue art needs to stand on its own, without the surrounding social context. If you view trash as art just because an artist told you, then the art isn't the trash the art is the artists explanation.

So, if you see a banana taped to a wall on a house when out walking, would you see that as beautiful art? If not, it isn't art according to my definition. The art piece is the whole thing, the banana and the explanation.

But many pictures can be considered art on their own without the social context, they are just beautiful and nice to look at. A banana taped to a wall doesn't pass that test.

Edit: So according to this definition AI art can be art, since some of those images can stand on their own as beautiful pieces of art without needing a social context.