What's the difference between "Alternative" and "mainstream"?
Well lessee... not the rhythm, it's practically all music in 4/4 with an accent on the 2nd and 4th beats.
Not the melodic system, they both mostly use tonal melodies with a blues influence.
The chord systems are the same.
So it's not rhythmic, melodic, or harmonic.
Uh... what else is there?
Arguably there's been no real change in music in the Western world since sometime after the turn of the last century. That's the whole Schoenberg argument: we've exhausted all the melodies available in a tonal melodic system. And although that's factual, it doesn't mean we don't all like a good melody.