there were fewer people total, so fewer bands - ie: less trash to sort through / increased popularity
there’s arguably more things to protest about nowadays but because of that there’s fewer things that both resonate with a lot of people and sound good at the same time
if everyone is protesting, no one is. there’s too many different slogans being called out, too many different groups to support (ie: buy the album or give them radio time), and many of those groups are at odds with each other.
technological advancement - radio is seen as a dead medium to many these days, there are far more ways to consume media than to listen to the radio. it may be that protest songs just dont air on the radio for that reason alone - their target demographic doesnt listen to radio.