Why can't rappers come up with their own music?

Today I was riding in my sister's car, and she made me to listen to
rap music. And every song that came on was a complete rip off of a
good rock or techno song. So stealing other people's music is okay as
long as you call it sampling? Do they just lack talent enough so that
they can't make up a beat or even their own lyrics- no, words for
their songs? I just find it sad that they are incapable of doing so.
And don't try to tell me that rock or other music is the same, because
its not. People who play REAL music (a.k.a. not rap) actually have
talent, unlike rappers. Have you ever heard "Lil Wayne" live? I saw it
on TV once and it wasn't exactly good... or even okay. I bet that if
most Lil Wayne fans only ever heard him live and without computer
effects to make him sound better, they would hate him.

Some examples:
Kanye West's "Stronger" stole from Daft Punk's "Harder, better,
faster, stronger",
T.I.'s "The show goes on" is totally stolen from Modest Mouse's "float
on",
Nicki Minaj's "Check it out" takes from "Video killed the radio star"
by The Buggles.