Pascal was the language of choice over at Apple in the original MacOS days, and as Mike has noted Turbo Pascal was popular enough on the PC; it was more, I think, that the UCSD-style language-environment-as-OS paradigm never caught on in the microcomputer world. Early consumer micros of course had ROM BASIC, but once you got past that to a reasonably full-featured operating system, there was no compelling reason for it to be tightly coupled to one particular language/compiler when it could just as easily treat compilers as Yet Another Program and support arbitrarily many.