Apart from the reasons already mentioned, there's also the OS dividing line (Mono is still treated like a redheaded stepchild on Unix) and possibly memories of

Apart from the reasons already mentioned, there's also the OS dividing line (Mono is still treated like a redheaded stepchild on Unix) and possibly memories of some incessant trolling/spamming a few years ago. I'm actually more surprised that SML seems to be completely restricted to academia nowadays. Standardized language, several decent compilers available, used in introductory books...