Western Europe used to be much more of a dialect continuum. Every village had their own dialect, and you could understand everyone around you.
But if you went from Castile to Paris, you'd go from hearing Spanish to hearing French. It's just that between them, you had dozens of intermediate languages/dialects that transitioned very smoothly. It's not like today where if you cross a border people go from speaking French to speaking Spanish.
A large part of the nation-building project in Western Europe was to force everyone in the country to learn and use some standard dialect. So very few people now speak Occitan, Picard, Burgundian, etc., and instead speak standard French.
To be fair, the dramatic nosedive in quality of GoT happened when they ran out of source material and had to wing it.
3-body problem is a finished trilogy, so it could all have the quality of the first seasons of GoT.