There's a whole science of how natural sunlight differs from leds (and its biological effect) and how to recreate it. I believe SAD lights try to replicate sunlight, but generally modern LEDs, even "warm" ones are missing key wavelengths and have a different profile from sun/sky light. There are now LEDs much closer to real sunlight, but they are also more expensive (though arguable not more so than knocking out more windows.

What I'm surprised at is how rare fake windows/skylights are. I mean, such products/companies exist, but they seem to be relatively niche, and accordingly expensive (as in "call our sales team for pricing" expensive), not really ready for your usual DIY/domestic consumer.

I think what we really need is monitor/TV companies producing low-res, high lumen screens for this purpose, hopefully mass produced. I think Sony has produced a "passive" screen ("the Frame") , that is effectively a matt tv mean to display slow/static images to replace hanging pictures (and even stuffs the electronics in the wall to keep a low profile), but it's still a luxury niche.