Those time periods are very different, but I think you're missing what Free League is doing.
One criticism of Free League Twilight 2000 is why is Sweden a setting along with Poland, instead of being all set in Poland. And it's obvious to me. Sweden is their home country, it's what they know, and there's an expectation of what people at their table want to play.
I hate to use a reddit term, but it's like American defaultism. Is it an oversight? Sure. Is it bad? I don't know, I don't care about Vasean. If I run a Viking game, would I be expected to explain what Valhalla and a Valkyrie is? How about an Egypt themed game or a samurai game?
No I see what they're doing and why, I just consider it extremely low-effort, a bad setting, and only requiring a modicum more effort to have done in a significantly better way.
Again, if you're just creating "the mythic north" just create your own Donut Steel not-Scandanavia.
For a Viking game, yes actually. A quick primer on Valhalla and viking religion in general I would absolutely expect to be included. You don't need to reprint every single Epic about the gods, but a brief paragraph/two paragraph summary of who are the major gods, how they work into viking life.
Or in other words, there should absolutely be an explanation of why its so important for Viking warrior to die gloriously in battle.
For a Samurai Game - again, I wouldn't expect the need to have a complete 900AD to 1900AD complete dynastic breakdown of every Emperor and Shogun. In this case you'd probably be setting your Samurai game either as a political jockeying contest under a Mikado or as a game of war involving Shoguns, or perhaps combining the two, so I'd expect at least a quick primer on "This is how Samurai fit into society, this is how Samurai would act, this is what it means to be Ronin, why couldn't an out of work Samurai just become a merchant" etc.
An Egyptian game, again you don't need to cover every Pharaoh or every dynasty, but is this Bronze Age Egypt? Iron Age? Classical? I would also expect a quick run down of Egyptian religion and culture.
For a pirate game in the carribbean, you don't need to cover every technical innovation or politics but "During this this period, the English and French were are war. During this period, the English and Spanish were at war and allied with the french. During this peroid, Everyone was supposedly at a very tenuous peace" and the disposition of major Islands.
Or if you were doing a Crusader game, a very fast break down of the rough political map of the Crusader Kingdoms between crusades would be absolutely vital.
edit: You don't need to constrain players/GMs to slavish historical accuracy, but if you are setting your game in a real historical period and not just an inspired-by fantasy setting, you need to provide GMs. the tools to take real-world events and translate them into their AU; If they ignore cetain historical events, how ignoring those events will affect later ones.
Speaking in very broad and general terms, european settings written by europeans are ashamed of their history and culture. The ones who aren't are super-nationalistic and offended that you're not already aware of what King Sharkfart did back in 1469.
P. Much this.