First of all, food is the most important thing. If there is no food, or if there isn't enough, than the crocodile population cant expand.
Second,humans are endangering many habitats (including the alligator species). By pollution, logging, and other stuff. We are destroying ecosystems and animal habitats very quickly.
Finally, crocodiles are ectothermic reptiles. They rely on the sun to heat their bodies. If a crocodile was in an area where the sun is a limited resource, then of course that could be a limiting factor for a crocodile.