Art used to be a noble thing. Almost by definition it was preeminent in a society; the pinnacle of what a culture had to offer. It strove to bring people higher and give them something to aim for.
And then postmodernism happened, which ushered in moral relativism, which brought modern art and semantics. Suddenly everything was actively questioned, which sounds good but isn't. Postmodernism makes everything relative and from that, nothing has any fixed meaning or value.
Normally, it would be accepted that the Sistine Chapel has more artistic merit than bottles of piss. Postmodernism demands proof to accept this. Feeling very clever with itself it can demand proof of anything and, when every issue of quality is reduced to the inevitable one of a preference by consciousnesses, Postmodernism can say 'well that's just like... your opinion man.'
It's the smug doctrine of the teenager who has just opened a dictionary and suddenly finds any definition of a word can be slowly chipped away at until all meaning is lost. Sadly today this cynicism is preeminent...