Because they weren’t necessarily always harsh, cold environments. The global temperature has fluctuated significantly in the last 1000 years or so. We had a medieval warming period from about 1000AD through 1200AD, followed a couple hundred years later by a “little ice age”. Technically, our world is still in an ice agethough the last 12,000 years or so have been remarkably stable compared to the longer scale geological timeframes ice ages generally span. Good thing our dependence on fossil fuels has upended our real handy metric for tracking this kind of stuff so we now have basically no clue wtf is going to happen climate wise in the next 10,000-12,000 years. Warhammer 40k is very optimistic about humanity lasting that long.
Because they weren’t necessarily always harsh, cold environments. The global temperature has fluctuated significantly in the last 1000 years or so. We had a medieval warming period from about 1000AD through 1200AD, followed a couple hundred years later by a “little ice age”. Technically, our world is still in an ice agethough the last 12,000 years or so have been remarkably stable compared to the longer scale geological timeframes ice ages generally span. Good thing our dependence on fossil fuels has upended our real handy metric for tracking this kind of stuff so we now have basically no clue wtf is going to happen climate wise in the next 10,000-12,000 years. Warhammer 40k is very optimistic about humanity lasting that long.