It has to do with the music industry.
Heavy Metal isn’t so much about political correctness as it is “rock and roll”.
Communists and by proxy hippies, didn’t like rock and roll, until they were able to co-opt it. Before that, it was juvenile junk and the product of capitalist Westernism.
Recall how they hated it when Bob Dylan went electric. He was supposed to be the spokesman of his generation.
The U2s, Pearl Jams, Radioheads, and REMs have the “right” politics. You have to get on the air sometime to become “big”. Plenty of other established acts don’t get the call.
Punk began as a backlash against hippie jams and political correctness. Legs McNeil has said as much. While Wayne Kramer and John Sinclair try to wear Sinclair’s “White Panthers” manifesto on the sleeves of the MC5, they were routinely called out by the hard left for not walking the walk. They merely were marketed as “radicals” by John Sinclair. Getting booked at the DNC 1968 convention helped (although the crowd had been told to expect the Beatles or the Stones).
There are left wing and even Communist sympathizing country artists. Kris Kristoferson, Steve Earle, Dixie Chicks, others.
Johnny Cash’s family seems to be to the left of his own political stance.
Not everyone feels compelled to beat their audiences over the head with their politics.
I could never figure out Johnny Cash’s politics. He was always anti-war, no matter who the president was. But he never publicly denounced any politician as far as I know. He was friends with Clinton AND GWB. He insisted in his backstage riders that an American flag MUST be on stage with him. My guess is he was a conservative democrat. Can’t imagine him giving concerts for pro-abortion causes, like his daughter Roseanne Cash.