Because the same laws that protect the artist with copyright also protects the code that I write as a hobby or release under an open source library to ensure th

Because the same laws that protect the artist with copyright also protects the code that I write as a hobby or release under an open source library to ensure that improvements to my code come back to the library. Without copyright, GPL and its deracinates have no leg to stand on to prevent it from being incorporated into closed source programs and forever locked away. Sure, you'll be able to copy the application without copyright protecting it, but you'd be unable to modify it. It would be the success of the free part at the cost of the libre values.