compilers and hardware back then were way more constrained. nowadays compilers do stuff like optimizing code and stuff, so an assembled C program can be more efficient than ASM entirely written by a human by hand.

but at that time it was typically more efficient for a human to manage all that low level logic on their own. most games on old consoles liek the genesis are done this way. Sonic Spinball is an exception and was programmed in C, but it has performance issues because of it IIRC