Why does mainstream music suck so much?

I listen to metal, mainly dream theater, metallica, slipknot, avenged sevenfold, megadeth, iron maiden, ac/dc, five finger death punch, system of a down and a bunch of other artists even including johnny cash. I can't help but notice that todays mainstream music just sucks. There's no diversity or effort put into making good songs and in the end everything sounds the same whatever happened to real artists like johnny cash, the beatles or freddy mercury. Its all about fame and money and no one wants to make real music anymore. I'm 15 btw