Mostly due to gaytar hero and the fact that it teaches you the basics of playing a guitar then most just give up playing because it's not like the game and you have to learn where to place all your fingers for the correct sound. I was playing guitar way before the game came out and people are like "I can do that better on gaytar hero", whoop de doo, I don't give a shit if you can play it on the game.
Aside from that, glad I picked up on how to play drums and keyboard as well, then I have more tards walk up to me if I play the drums saying they can do that on rock band, I don't give a shit there either. You can play it on the game, so what? I don't care.
TL;DR people play because of guitar hero or rock band then end out giving up after they learn it's not as easy.