[dgeiser13]

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.

[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.

[pandaman]

The article actually explains it: with 2 staircases requirement the cheapest[+] option is to have the internal shared corridor and thus you get just one external wall for an apartment in general (unless it's in a corner where it gets two). If you arrange a bunch of bedrooms along the wall you end up with an internal corridor, wasting space, and making your whole apartment looking like a sleeper train car.

Houses, on the other hand, have 4 external walls at the very least. Not to mention most 4+ bedroom houses are 2+ stories as well.

[+] It might be also required to have staircases at decent distance, as a second staircase going through the same stack of apartments is not of much use as it's likely to be blocked by fire at the same time as the other one.

[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.