Deep ketosis probably has something to do with it as well. Human babies are the fattest land animal, even more so that baby seals. That same brain we use to hunt is made of fat, ketones, cholesterol. In northern climates the only food source in winter is large fatty mammals, megafauna, with a much higher percentage of body fat than smaller mammals. You are warmer in ketosis, higher internal temperature, with higher heartbeat stroke volume. Like having an internal oil fire instead of internal plant-kindling fire.

I expect body hair loss was influenced by sexual selection, which can be a rational or irrational, an aesthetic or utilitarian, feedback loop. I like to think a newly unlocked higher value set led us to grasp toward something more aesthetic. Probably a meta-mix of reasons.