Death by sunlight? Bad from an evolutionary point of view.

Trolls die as soon as they're exposed to sunlight. Why didn't such a severe evolutionary drawback eliminate the species long ago? How do they manage to live for between 1000 and 1200 years, when being outside for just a moment after sunrise will kill them? Given their size, I imagine they might have difficulty always finding a cave to hide in that will fit them until sunset, especially given their limited intelligence.

And let's not forget that in southern-mid Norway the sun is up for around 20 hours a day in midsummer, leaving only 4 hours of darkness for trolls so get out and hunt for food. This would also preclude the survival of trolls in northern Norway, where the sun doesn't set at all for several months in the summer, unless they can do all their hunting in the spring and survive on that while they hibernate in the caves in the summer.