Numbers, poopster. Pure and simple. In the year and a half I've been playing even I've seen a slow and steady (well, OK, except for the AW influx) rise in the numbers. Evenings US time it's regularly pushing 600 in the MA. Nearly fell off my chair when I logged in a couple of weeks ago and saw over 600 people on the pizza map. And now a lot of the maps are straining a little at the seams. I love the Mindanao map for the terrain, but it feels really crowded now because the fronts are so narrow that ganging is the order of the day everywhere. The same with the islands map. The one that is, for me, starting to work really well is the Pizza. With the kind of numbers you get in there in the evenings (again, US time, earlier in the day it can be another story, although not anywhere near as bad as it was a couple of months back) you get big fights, and I've also had some of the best one on ones or small group fights anywhere (except, of course, for the CT); the kind that leave you shaking and wondering how the hell you managed to survive that. (Big drawback with the pizza map, of course, is that you have to face all the people who haven't turned their monitors on and yet are complaining they can't find a fight. if you can't find a fight, even in the big map, with 600 other people, you need to go back to playing Quake).
So it will be interesting to see what, if any, difference the new maps (whenever they appear) will make.