I was thinking the same question and the reply would probably be "performance". I don't think untyped Racket can currently compete with SBCL and I'm not sure they'd be interested in Typed Racket. But I'd love to be proven wrong on both of those things ;)
But that's not the reason. Personally I find Lisp superior in most respects, but I don't think it's a good place and time to argue on Lisp vs Racket and similar topics.
