To add to the other reasons - the CS compiler optimizes different forms and Racket is currently optimized for it's own compiler. To give a concrete example, taken directly from the racket blog [1]:
> For example, Racket BC makes dormant code relatively
cheap, so Racket libraries generate a lot of code. Future
Racket libraries will likely shift to take advantage of
Racket CS’s cheaper function calls and dramatically cheaper continuations. One day, probably, Racket BC will no longer be a viable alternative to Racket CS for most programs.
> For example, Racket BC makes dormant code relatively cheap, so Racket libraries generate a lot of code. Future Racket libraries will likely shift to take advantage of Racket CS’s cheaper function calls and dramatically cheaper continuations. One day, probably, Racket BC will no longer be a viable alternative to Racket CS for most programs.
[1] https://blog.racket-lang.org/2020/02/racket-on-chez-status.h...