Good question. I'd expect it to be a knock-on effect following one or two very successful books and scripts but maybe also the publishers and production companies on the lookout for more.
Some people with scripts in their kitchen drawers got their chance. Others build on that.
I would not think it to be the Scandinavians somehow being special. We don't have a special gift for broody and dark, some of us simply got the opportunity to write and publish stories. Our societal environment plays a part, of course, but that's not why. It's just more of the same.
I'm fairly sure that pretty much anywhere else in the world there will be another genre waiting. Cultural and sociological coincidences will determine if any of those get the chance.