A) Compiled lisp is typically faster than C for complex applications due to better handling of complexity. Erlang is typically faster than C for highly threaded applications, sometimes even when interpreted. For something that spends its life in tight numeric loops, compiled FP languages tie with C.
B) C is one of the most error prone, finicky, hard to code/maintain languages in existence, only next to assembler. Given that C is "portable assembly", that stands to reason.
C) FP has been around long enough and been used enough to have solid practical underpinnings. Yes, any new language has its wankery (whether imperative, OOP, stack, FP, etc, and including C's history), but practicality fights against it.
D) C is incapable of scaling to complexity in terms of programmer load, without adding custom intermediate layers (ie, custom code generators or scripting engines, so why not use an already designed language?). FP is about the same level of effort to do easy stuff with and FAR easier for complex programs.