The main thing about cold blooded creatures is that they are just far less adaptable. If you move them somewhere significantly hotter *or* colder from what they are adapted to, they perform poorly.

They don't have a way to generate heat or vent heat nearly as easily as warm blooded creatures (generally) do. Some warm blooded creatues do better with heat dump than others (humans sweat, which is way better than the way dogs stick their tongues out).