One explanation could be that Vikings massively switched to renewable energy, recognized and apologized for their white privilege, and abandoned their Greenland settlements to the native population. The Vikings then returned home to found perfect socialist utopias.
Alternatively, it was warmer in the Medieval Warm Period than it is today, and the theory of anthropomorphic global warming is malarkey. It got too cold for Vikings to farm in Greenland.
As the holder of an MS in Statistics, I think the latter alternative is way more likely.
A Call for Healing
Democrats Call for Healing the Country