The Apple of the past never thought twice about people complaining about the lack of them implementing something that would be bad UX because they were confident in their design prowess.
As the sibling says you can turn it off, but even the non-windowed UI is still not well-adapted to the small form factor. Apple doesn’t put any work into it. One can hope that some improvements might carry over from the upcoming foldable iPhone, whose inner display will only be slightly smaller, but I’m not holding my breath.