A lot of progressive rock bands (like Tool) are hit or miss. Some people love 'em, some people hate 'em. It's a matter of the listener finding something in the music that appeals to them. Some progressive rock bands have that "thing" that some listeners have. Some people listen to Tool and think they lack melody. Some people listen to Symphony X and think they're too "cheesy". Some people listen to Dream Theater and hate the singers voice. It's different for everyone.
MTV is a company, and therefore, it is their job to make money. In order to make money, they need to have high ratings. In order to get high ratings, they play what the majority of people want. Unfortunately for us, the majority happens to be emo kids, "gangstas", and teeny boppers that love Ashlee Simpson and whatnot. All us metalheads get is that hour a week called "Headbanger's Ball", in which they play what the majority of metal fans want. If a band is played on MTV, they haven't necessarily "sold out". They've just grown in popularity. I've seen plenty of Iron Maiden videos on MTV, both during and not during Headbanger's Ball, and they have by no means sold out.
But, whenever a stupid trend whore sees a band like Dragonforce or Iron Maiden on MTV, they think "Oh, they must be popular, because they're on MTV. I wanna be popular, too, so I should wear a Maiden shirt since they're popular enough to be played on MTV." and this causes a lot of false fans who just wear band shirts because they're insecure bastards and wanna fit in with the crowd.
Oh, the wonders of today's youth.