There are always 1-2 full servers running, which means there's always at least one full game to join.
We have held these numbers steadily for years, inclining with patch releases, and steadying to 1-4 servers regularly. The only way for more people to play is to invite more people to play. Until then, we have a very reliable and stable community.
It may be small, but it's consistent.
The two main factors that influence the size of the community as I see it is the Crysis Wars Paywall and the learning curve. It's hard for us to retain anyone who doesn't have an attention span beyond CoD and Battlefield due to the learning it takes to play competently.