Art advanced along fine because there was no way to copy paintings and sculptures. There was no way to record a play or orator.
But that, of course, is no longer true. The advent of technologies to capture and distribute art has led to new forms of art, and with that an amazing situation where people have unparalleled access to the works of genius. However, those new forms also have a drawback: they can be easily copied and distributed without compensating the originator. So in order to keep being able to support filmmakers and novelists and musicians we need to shield them from this. Otherwise, they will stop making their works.
Who is going to spend 5 years writing a novel if they can only sell one copy?