Why are there so many processes for FME Server?

This is a good question to ask for sure. The main reason is one of software design choice. FME Server could have been engineered as a single, multi-threaded application and then you would only see one process. The potential problem with this approach is if a thread crashes, then the entire process crashes. We choose to separate each functional area into it's own process to avoid this and provide better fault tolerance. Google's Chrome browser does the same thing, where each tab is a separate process.

A really good question to ask is: are you seeing an impact to the performance of your applications? In most cases, there is no impact to system performance. If FME Server is installed to a machine that doesn't meet the minimum technical specification, then you may so performance impacts.