Also, just speaking for myself here, I wouldn't be averse to using a custom dialect of some kind, maybe even a novel Lisp that departs quite radically from the LISP-1/Scheme tradition for the sake of (for example) easier host integration, simpler GC, better/simpler optimization rules, or (most critical for game development) more reliable live debugging and hot code reloading. I could even acquiesce to building the whole game in SBCL, like Kandria.
So why Scheme? Just because we are here, surrounded by people who love Scheme.