Since 2014, house owners are allowed to have this kind of "mini house" built on their property. It's treated as a "real house", with its own address and somebody can live there and everything. However, you aren't allowed to skip the "big house" and only put an Attefallshus (or two of them, or three) on an empty plot of land.
This is extremely frustrating to me, since I cannot afford any of these insanely overpriced houses, but I would on the other hand be able to (just barely) afford an Attefallshus on an empty square of grass. It would be enough for me to live inside alone, albeit somewhat claustrophobic. Still, it sure beats being homeless.
Why do they force me to buy an impossibly expensive "real" house of a much larger size and to then have this as an "extra" home? Why can't I just buy a cheap plot of land and have the Attefallshus delivered/installed on it, and live like that, with no "main" house? What possible reason could there be for them disallowing this? I really don't understand their reasoning. They explicitly disallow it, but don't explain why.
I would've asked this in the "Sweden" Stack category, but there is no such thing. Maybe there's a similar law in the USA or something, or you could maybe give an educated guess.
If you are curious what they look like, this is an example of one (bunch of photos): https://www.bjurfors.se/sv/tillsalu/stockholm/stockholm/alvsjo-herrangen/noaks-vag-3d/#bilder