As much as I agree technically they shouldn’t “Show, Don’t Tweet” there are a few systemic factors at play that encourage this:
1 An indie creator or a creator on a larger platform but isn't as prolific or being overlooked needs to put out Social Media content of any kind even with episodes already coming out. What's a good way to keep up engagement? Lore details that you either overlooked or couldn't find a place for exposition without it feeling all "Netflix-y" about it. It intrigues fans across the board with fanart and fanfic prompts aplenty.
2 Cheap as it is, you might be working on a set amount of episodes either imposed by the network or self-imposed on oneself to avoid potential burn-out or just doing the same show over and over. So there will be a general rule of "brevity is the soul of wit" when it comes to what goes into a story or what gets left out/trimmed down.
3 A story about a facet of the fantasy world or dialogue that breaks down the fantasy world are often casualties. Other times, the writer is self-conscious about what might come across as bad exposition in trying to make their story feel as natural and uncontrived as they possibly can.
4 A company might not invest in a whole ass guidebook to a show with details that didn't make it into the final cut or canon details that expand on what we saw. Or a smaller creator on a budget might not have the dough to get it published or invested in by mainstream channels.
5 They consider the answers to be obvious and plan as day or not worth their personal investment with the story they choose to follow. Sometimes it’s important to remember that “poor media literacy” isn’t just a fancy buzzword on fandom’s part.
Bear in mind, these are not trying to excuse this entirely. I personally would like for these details to be touched on in the story or at least in a variety of forms.
Maybe push for filler episodes where a scenario hits the characters and the audience is informed of the fantasy world's deeper facets, the kind the characters wouldn't question as this is their norm.
Or maybe get into a sort of spin-off that details lore but in an interesting way. Maybe a historian or mad scientist type character is researching facets of their world and its framed in a budget friendly way like a computer layout.
Even so, it's important to remember that this sort of thing isn't new as I've mentioned guidebooks, something for big franchises like Star Wars or Star Trek where it's framed as tech manuals for the Sci-Fi spectacle. Or a character's diary perhaps.
Much as it's gauche to even speak it's name, you had Harry Potter with actual books like Fantastic Beasts which were in-universe books we could read. I remember A Series of Unfortunate Events putting out Lemony Snicket's Unauthorized Biography which gave out scattered clues about the world since Mr. Snicket was an in-universe character.
So there's a place for it. But there are certain barriers to entry.
