If the populations that you're talking about are the famed "blue zones," then the most likely reason for it is poor record keeping: https://jheor.org/post/2682-

If the populations that you're talking about are the famed "blue zones," then the most likely reason for it is poor record keeping: https://jheor.org/post/2682-ig-nobel-prize-winning-research-longevity-claims-may-reflect-lousy-birth-and-death-recordkeeping-more-than-accurate-human-lifespans https://jheor.org/post/2682-ig-nobel-prize-winning-research-...