I don't think it's about 'earning' enjoyment of music, I think it's about cultural signaling: when you fill out a Facebook profile, you're making a public statement about who you are. ~340k people _is_ pretty much an 'epidemic,' if you consider the actual audience of punk back in the '70s.

By putting "I like Joy Division" on your profile, you're making a statement that you're not a follower, you won't stand for authority, etc, etc.

At least, that's what people like to think.