Earlier quoted context omitted.
In the US the nuclear family is usually two parents and two children. The parents share one bedroom and each child gets one. In Asia I would guess families make room for their older relatives which would mean an extra bedroom is needed. Immigrants to the US typically do that but I think it's uncommon among the rank and file Americans.
I think in the US a home office and a guest room is also usually needed, so 4-5 bedrooms makes total sense. In fact 4-5 bedroom single family houses in the US are extremely common. What I don't understand is why apartments always seem to stop at 2b or 3b.
Apartments are for dense housing, big apartments aren't dense, therefore look elsewhere for your large apartment, I guess. You could have 4 tiny bedrooms, I guess, but that's weird too.
It's nice to have an office/guest room, but if you're raising a family that needs three bedrooms in apartments, you're compromising.