Other languages are much easier to work with for the sorts of programming tasks useful in web development (e.g., string handling), and the things that C is good

Other languages are much easier to work with for the sorts of programming tasks useful in web development (e.g., string handling), and the things that C is good for (e.g., direct memory access, extreme optimization) are not terribly useful for web development. Getting every last bit of optimization out of a C web program isn't a practical advantage if there's a much larger time delay due to network access! That plus it's much easier to make some really awful mistakes in C than it is in languages more often used for web development, so why risk using C if what it gains you isn't helpful?