>>86600
AFAIK giant humans were populating earth in previous eras, either dvapara yuga or treta yuga. With each era people become less spiritual, smaller in stature, dumber, less moral, uglier and their life span gets shorter.
Era changes are marked by cataclysmic events that wipe out previous civilizations (like a comet causing ice age; global flood), thus giants are extinct in our dimension / the part of earth we are able observe.