I can only guess but art is now considered to be inherently subjective. So you there's no way to make statements like "picasso is better than jackson pollock", or "cubism is not real art".

Going further there are a number of works meant to probe the exact limit of what we're willing to consider art. I recall a couple interesting ones:

1. An artist took a shit in a can and sealed it up: https://en.wikipedia.org/wiki/Artist%27s_Shit

2. I recall there was an artist who took an existing book and changed the author name to their own, I can't find a link right now though.