TwoSix
Everyone's literal second-favorite poster
Yep. If I stick my hand in a fire, it's going to hurt a lot and I'm not going to regenerate it. If a troll sticks its hand in a fire, it's also going to hurt a lot and it's not going to regenerate it. I still use fire, why wouldn't the troll?For a more serious answer: Fire is wildly deadly and destructive, yet we use it extensively and often with great carelessness. Why would trolls be more sensible humans?
Just because trolls regenerate doesn't mean they don't have a pain response and learn to deal with it, just like any other creature. The convenience of light, warmth, and cooked food vastly outweighs the idea that killers might invade my cave and try to use my firepit against me.