It comes down to 2 things, money and time.
More servers could ( potentially ) mean that we have to start investing hard cash in the project. Right now it's limited to Talad paying for his site and me paying for the forums. We have been very luck so far to find hosts that are not only willing to donate hardware but also the bandwidth and their skills in setting up the server. However, if we want to start working on some sort of server farm that is going to require $$$.
Secondly, I know that most of the developers have regular jobs and many in the software/hightech industries. It's not always easy to work 8-10 hour days staring at computer screen and then come home and do the same when working on PlaneShift. Some of us do it better than others but it's all about doing it when it's fun to do.
We are getting a bit better organized now with a proper testing group that should help fix some of those 'post update' jitters that we usually have.