I recently began to use StackExchange sites and I'm really happy with them, both contributing and receiving help.

But I have realized that ServerFault questions and answers receives much less attention than StackOverflow or SuperUser, for example.

Is there a direct correlation between the activity of ServerFault and its number of users? Are there other factors such the kind of questions asked (mainly sysadmin stuff) or a lack of interest of experts on this area?

You may think this is a very open question subject to discussion, but I think developers can access traffic or usage data to give a general idea. I'm interested on this rather than subsequent explanations.

EDIT:

Of course, subsequent explanations are welcome as well :)