That has me wondering how much average height and square-cube law implications like surface area ratio changing what they consider "the norm" has to do with it.

BMI as a health metric is downright lazy mathematically in that it doesn't use a cubic portion and thus gives more undue "slack" in its judgement for shorter and less for taller.

I am uncertain what aspect if any dominates. It could be that without sufficent HVAC exposure the local climate causes the body to adapt and dominate. Granted not allowing that adaptation may not just be "softness" and "disconnection from nature from arrogance". Apparently according to some accounts colonialists in the tropic were looked upon by natives as fools and lunatics for being physically active during the hot and bright sun instead of resting then and saving activity for when it is cooler.