The real problem is families in the US don't desire apartments and so no one builds apartments that families would desire to live in, thus perpetuating the problem.
Also, in California, "apartment" means short-term leasing and is usually full of young singles, couples, divorcees, and retirees. It is often a big building with many studio, 1, and 2 bedroom units. A similar multi-dwelling structure with individual unit ownership is referred to here as a condominium (condo). These often have slightly larger units since they are targeting the home-buying family rather than the itinerant renter.
In SF Bay Area suburbs like Walnut Creek, there are also neighborhoods with town-homes. These are like condos in ownership structure, but often only have 2-3 units per building, wrapped with a small private yard maintained by the owners. And these lots are in turn surrounded by larger common grounds, which are maintained jointly by the HOA for the whole neighborhood.
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.
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.
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.
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.
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.
Here's a recent story of what happens when Asian family sensibilities move into a typical American neighborhood
https://www.nytimes.com/2026/03/12/realestate/massive-home-a...
neighbors were upset about this addition, built to house aging parents
https://wjla.com/resources/media2/16x9/1280/986/center/90/fd...
There’s also a pretty strong effect in the US that selects towards raising 4+ person families in a house (whether rented or owner-occupied) if at all possible, so a 4 BR apartment is likely to be occupied by the (relatively) rare tenant who prefers to live in an apartment, but more likely one who is forced to by lack of option. I suspect this effect is much smaller in Asia.