One could make a "theory" easily, to argue that musical skills improved
mating opportunity in early humans.
But we don't have to rationalize every human behavior by evolutionary
selection. You can have "emergence", that is, when human intelligence is
complex enough, new behavioral traits emerge. Evolution is essential in the
sense that it provides human with the perceptive foundation to appreciate
music, but it is not the direct formative factor for such advanced
intellectual behaviors.