It is not about preference, but because of regulation. Nowadays the government demand is that each child needs to have a separate studying and sleeping area. If a sliding wall in a room counts as a separate area is up to the officials' discretion.

On one hand, all of this is understandable, but on the other hand these policies do indeed raise the cost of having children.

I have never heard of a government demanding that. Where does that happen?

What government does that? That's something new to me.