Because I don't know how modern Lisps can do it (I believe there was hardware like lisp machines made specifically for Lisp that would deal or help with memory allocation/reuse as well as some code generation).

I honestly was curious if the OP had some insight that I did not. I realize re-reading the comment it sounds snide but I didn't want to assume the OP's knowledge.

For all I knew Racket could have some ability to avoid GC.