[qurren]

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.

[toast0]

Mostly US apartments don't go beyond a certain size, after that you need a house or maybe a townhouse. Double maybe a condo, but those usually don't go bigger than apartments either.

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.

[sokoloff]

Because there’s a heavy bias for people who have use for 4+ bedrooms to also not want to live in an apartment building.

The reasons vary, but I have lived in Boston/Cambridge area for 40 years and can’t think of literally any of my friends who raised a kid past the age of 3 in an apartment, despite many of them (including me) enjoying the apartment life while young and single. But, literally as soon as we could [barely] afford to, we bought a house and only then added to the family.