for most animals in the wild, their life expectancies are shorter. i would guess that it would have to do with their bodies having to function at peak performance 24/7 to survive. im sure it drastically speeds up the deterioration process of their cell health, which would lead to more rapid death. also, statistically, when youre out in the wild surviving, your life expectancy goes way down. you could live for a good 14 years and get killed by something bigger than you.