It's no different than when all the rockbands of the 60s and 70s started to change their tune after the Vietnam war and the stagnate cultural state in America. Their music did not match the standard of pop music of that time, but they quickly became popular because many of their songs reflected what the people felt in that era. So bands like The Doors, Water Creedence Revival, Bob Marley essentially started a cultural reform like Samurai. It's not widely unbelievable to think a hardcore punkband reaches mainstream success (cough, The Clash, cough, Green Day, cough, Sex Pistols, cooooooooooough!)