That dynamic was exactly why I moved from Scheme to CL many years ago (full disclosure, Clojure is my daily driver, now). I loved the minimalism of the RxRS documents, but they really only covered the small core of the language, and then all the implementations were completely different when it came to libraries. And those differences always needed to be understood in order to write real-world programs. SRFIs helped, but adoption was spotty. Every multi-implementation language has some of that, but Scheme had more than most. For me, the choices were to use a very full-featured Scheme like Racket (which is great) or go to CL and then use something like SBCL. I went with CL and later jumped to Clojure (which, IMO, is a better, more modern Lisp that fits better with today’s multi-core hardware than either Scheme or CL).