My additional theory on top of that was that in warm countries nature often provides free food. Don’t need to hustle. Don’t need to hustle to create shelter also. So the environment sort of discourages any extra effort.
At the same time there could also be some with natural flexibility to adapt to more extremes than others, realistically outside the realm of one extreme or another dominating, but instead for some the ability to adapt is what's extreme enough to be uncommon.
Sometimes maybe even beyond the range of both cold lovers and warm lovers combined.