I would argue Falena, and this fuck-ass family, can justify building a modern-city for the birth of Cheka while refusing to develop other, densely, populated villages in SunSav:
because this project was approved by their inner political buddies.
Because it's a frivolous use of funds, used in a way that doesn't actually benefit anyone except for the, already, insanely rich. If anything, this project, to develop the capital, was put on the fast-lane because it made them look good to the outside world.
"We want to preserve nature and water, which is why we developed this big city and golden, water fountain right outside the royal palace. Don't look past this area where all the tourists and colorful vendors live. You're not allowed to do that, What do you mean 'why'?"
"Why does this water never evaporate? Magic silly! 'Why can't we do this for the rest of the country?' Well......"
Briar Valley is explained away by being cut off from the world, It doesn't need outside intervention because it's already self-sustaining due to Fae magic being different from normal magic AND having an in-grown economy. It doesn't NEED the outside world to survive. Sure, some modernity would be nice, but certain modern amenities would not mesh well with the supernatural shit going on over there (read: phones, the Internet, some electric devices, etc.,). And, with B7 explaining the Human-Fae War and how the country is still, do a degree, recovering, it makes sense as to why they'd be hesitant in letting people, and new age inventions, in.
Was there a war? Is there corruption? Is there economic trade with outside countries? Is there mass immigration out of the country because of the shit working conditions? Similar to the border crossings from Mexico to America?
Does Yana realize having more than one place with a fucked-up way of life is more realistic and accurate to real-life? Having the Scalding Sands and SunSav, hell even Pyroxene and the Coral Sea, have some kind of corrupted underbelly is INTERESTING. Having them all being corrupted in different ways is INTERESTING.
Trying to frame every country as "A great place to life except for [insert one bad thing here]" and not elaborating is LAZY. It’s LAZY AND BORING.