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
Aha by mainstream I mean lady gaga, justin beiber, katy perry and all
that crap