A patent for an invention lasts for 25 years from issue. That patent could have involved a great deal more education, research, and just sheer hard work than any piece of music, and furthermore may continue to be essential to much of humanity for centuries after it has lapsed.

Now, why should one kind of inspiration, music, be allowed to bankroll the originator and their descendants, yea even unto the seventh generation, when a patent often expires before its originator, especially if a lone inventor, can even get back the investment put into it?

Copyright, like most patents, is intended to preserve the value of the intellectual property for large corporations. If it helps the small operator on the way, that is just a side effect.