Interestingly ClojureScript's are self hosted: https://github.com/clojure/clojurescript/blob/master/src/mai...

The JVM Clojure story is probably just that the data sturcture implementations were done very early in the history of the language before all the type etc directives were there.

they are indeed, what else would they be written in?

I'm having trouble connecting this with what I said...