I think this was the most uncomfortable I've ever been watching a movie.
There are so many questions left open, this abyssal mass of possibilities hanging over every scene - when there are no rules of engagement, no explained logic, any horrible thing can happen.
Obviously, I can't speak to why Lanthimos makes the creative choices he makes. To me, the stilted dialogue and sterile environments are there to intensify that abyssal mass - one perfectly clean room after another, one stilted, transactional conversation after another, one perfect family and perfect house and this and that - so when it's upended, when the unknowable shows its face, when horrible things happen, the shock of it all is exacerbated.
So many possible meanings, lessons, themes - it sticks with you for a few days.