The reason that we have copyright is because before it existed authors would publish a book and find that other publishers would also publish their book - but without having paid them to do so. This limited the ability of publishers to pay authors.
This is from a time before music could be sold in any way other than sheet music (or live entertainment obviously). And in fact sheet music was also ripped off. Hence copyright was invented as a way to allow authors/publishers to get paid.
The system is not perfect. Gasp! The alternative has distinct downsides, as even a moment's thought ought to suggest.