Sounds like they were more British, than German - logically we should copy our alien neighbours, emotionally b**l*cks to that, im not growing weeds, lets go hunt a walking mountain.....It could well of been climate, although there remains the puzzle that if Neanderthals and H. sapiens were living fairly closely (assuming they did interbreed) then why didn't they simply copy whatever hunting/food gathering advances H. Sapiens were making? Were they disinclined to follow an alien culture or did they lack comparable intelligence to fully understand their rivals techniques?
I am reminded of the fact that Scandinavians settled Greenland several centuries ago, in a warmer period. When the climate become less suitable for agriculture, they simply died out - even though natives carried on living there, sustained by fishing. For some unrecorded reason, the settlers did not adopt fishing.