The question starts at: Why do studios continue to sign 'rappers' to movie roles?

Answer: $$$$$$ at the box office.

Think about it...Buta Rhymes in Halloween, JaRule in Fast and the Furious (and the sequel), there are people that are going to these movies JUST to see their favorite MC spit 3 lines in the first 3 minutes. Much better than casting Johnny No-Name from Idaho who's a great actor, but doesn't have any clout for a name. It sucks, but that's how it is.

Same goes for all these feature length cartoons. Can't have Betty Who's-That play the voice of the curious cat, it's gotta be Cameron Diaz, Jennifer Aniston or Julia Roberts. Think about it, would you have gone to see Shrek if Mike Meyers, Eddie Murphy, Cameron Diaz and John Lithgow weren't in it (well, maybe not John Lithgow)?

So in a sense, I kinda agree with Sam Jackson because I don't care for this new trend either.