We always played with at least 5, and quite often with a close to full team. So there's that. We also play against lots of other teams that has close to full teams, and this is fifa on PC, where there is way less people playing. Keep in mind, you get matched up against clubs where they have around the same amount of players...
Also random 3v3, is not the same as Clubs anyway. I want to play with our own players, own club, and climb up the leagues and cups with it.
Look at our stats here, and see how active we used to be
http://www.neogaf.com/forum/showthread.php?t=897860
and we had other players on top of this, that only dropped in every once in a while as well.