mainly because the CLs aren't clojure i.e. AFAIK don't use persistent data structures, and don't focus on robust concurrency primitives, don't have STM, etc...
But if there is a CL out there that does all that I'd give it a try tonight :)
You could try LFE[1] instead if what you want is concurrency, but it still is a hosted language, the only difference being that it relies on Erlang instead of Java ecosystem.
Lisp (what is a Common Lisp "flavor"? Racket is Scheme) has answers to all... Of course the benefit of Clojure baking those things in is you can rely on them in other people's programs, but still idiomatic Lisp seems to do an ok job managing state, especially compared to other languages. Plus its other features that Clojure lacks might make the tradeoff worth it.
Racket is not Scheme (anymore). Racket is a Lisp-1 with lots of different features and "batteries included" stdlib. It's a "descendant of Scheme".
Worth taking a look into definitely, but it doesn't have STM and "persistent data structures" which jfaucett seems to want. It does have solid concurrency and parallelism primitives, though.
But if there is a CL out there that does all that I'd give it a try tonight :)