A couple of reasons: - The use of C requires much more skilled developers then say Ruby or PHP. Note I am not saying smarter, I am saying skilled.

- In web development - for most products - speed of development and maintainability trump out right performance

- Most languages abstract away the machine architecture (Ruby, Java, PHP) and all simply with dealing with higher level primitives

- While garbage collection is available in C, modern languages such as Ruby, Python, PHP and Java have much nicer native implementations

- Web frameworks are far more advanced for other languages then C (RAILS (ruby), Yii(PHP), Django(Python), Grails(Ruby) just to name a few)

- The other languages have a much richer native types/and object models then C

Given these - there is nothing preventing you from using C for web development, given sufficiently experienced and capable developers.