#1.It's telling a story
Maybe it's telling the story of starlord's mothers life since she meet Jason(Quill's father).
#2.Disney wanted it to be kind of a musical
Disney owns Marvel studios and maybe they wanted to make a sort of superhero musical.
#3.Maybe the director liked the music
Maybe James Gunn (the director) liked this kinda music
#4.Maybe it's a coincidence
Maybe it's a coincidence.