1.) most rock/alt/pop music is made by 20-somethings for teens/early 20-somethings. their shared culture is the left-dominant education system, so not surprising any political messages in said songs would nod along with left-wing bromides.
2.) the owners/gatekeepers of entertainment industry are overwhelmingly left, so not surprising the aspiring performers mimic their politics. (recall that even the most successful band of the late 80's - thus, the band with the most industry leverage - guns n roses, had to beg forgiveness for their song one in a million that, 25 years before maga, expressed skepticism about the lib sacred cow groups, gays, blacks, immigrants.)
