Other reasons would include post-release support, which was better than Crysis 2, but not a whole lot better.
I am going to miss Crysis 2 & 3 very much. I know people who played Crysis 2 for 4-5 months after release and then only popped in occasionally afterwards.
Sooner or later, both C2 and C3 will have less players than one would want to, they will die(unless they are already dead) and players will move onto different games.
What games will you guys move onto? I am sure many will say BF3/BF4 or some COD game, but neither of those will be Crysis-like, no cloak, armor mode, always on power mode, no nanosuit. Crysis 2/3 may be COD clones, but they were still fun, and I don't think any game can ever *truly* replace them.