Most daemons are written in C. It's fast & robust. But if you are in a LAMP oriented company like me, and you need to create a lot of software in PHP anyway, it makes sense:
Efficiency. Reuse & connect existing code Think of database connections, classes that create customers from your CRM, etc.
Speed. Deliver new applications very fast PHP has a lot of build in functions that speed up development greatly.
Continuity. Everyone knows PHP (right?) If you work in a small company: chances are there are more PHP programmers than there are C programmers. What if your C guy abandons ship?