I get where you’re getting at since it’s a minimum standard of living. Two bedrooms basically means parents in one room, 1-2 kids in another. With two children being the default. Once you get to three or more, or for people who don’t want mixed gender siblings in the same room/heavy age differences, then the two bedroom becomes the three bedroom.
I definitely err on your side of the logic though. That is technically minimum. In reality, there’s enough money for that three bedroom, the rich just hoarde it all. Most landlords got nothing to do with that lol.