Real Science | The Insane Evolution of Hibernation

This is important because the hibernation process of ectotherms is passive, forced by environmental conditions (and which also requires massive adaptations like butt breathing), while torpor is an actively regulated phenomenon (although we still don't know the exact mechanisms).

To put it in a simplier way, an animal can arouse from torpor even if the enviromental conditions stay advers, while an hibernating ectotherm can only be aroused if the envrionmental conditions improve (substantially if the wether gets hotter).