The main competitor to C would have been PASCAL, and the drawbacks of standard PASCAL for low-level programming (a necessity on the computers of the day, where even ASM programming was commonly resorted to in order to eke out the best performance) were very well known. C was not perfect by any means (the segmented memory models on 16-bit x86 required non-standard extensions to support, for example) but it was a lot better than the alternative.

LISP would've been a total non-starter for serious use given its requirement for GC and being an interpreted language. Quite comparable to the dog-slow Java applets of the mid-1990s, and in fact even worse on early hardware.