The true purpose of copyright is to motivate the creators to continue creating in this sense. Creator creates song which is copyrighted and they profit from their creativity. Copyright expires. If Creator wants more income, use their creative mind to create more great works and copyright them. A creator’s great great grand children should not be profiting off their ancestor’s work.
Because of how quickly technology changes, software copyrights should be greatly decreased. Windows XP’s copyright expires in the 2090’s. Think there will be any hardware that could run XP in the 2090s? or even in 2050? I believe software copyrights should be 20 years. Look at the market for classic games which are no longer manufactured, marketed, supported or profitable (abandonware) yet the copyright holders often continue to enforce copyright.
Copyright, according to the constitution, is supposed to be limited, but it is continuously being lobbied for perpetual extensions. For instance, the Copyright Term Extension Act (aka Mickey Mouse protection act) was heavily pushed by Disney because Mickey Mouse was approaching the end of its copyright term and as 2019 approaches, you can bet that Disney will lobby for another extension of copyright