Rock used to be rebellious, but that aspect has become more of a joke over time. As Lisa Simpson put it (albeit not about Rock), "that's rebellious... in a conformist sort of way". Indeed, Rock is embraced by such a wide variety of people that really, it's only ever used very generically. Rock has become sort of a mythical entity as well, with The Power of Rock based on this. All you need to cause radical social change is a guitar, bassist, and drummer to rock out. The ubiquitous nature of Rock has made it more of a Dead Horse Trope than anything at this point.