What would you use all of the extra rooms for? One room for each person to sleep, a laundry room, a couple bathrooms, and a great room with living, dining, and kitchen is all you ever really need right?
More rooms is nice if you don't like being on top of every single other person in the house all the time, without having to go to your bedroom (aren't we supposed to only go there for sleep, for sleep-hygiene reasons?) to escape. In recent houses this means using ~3x the space you actually need to accomplish that, mostly by adding a room or two in a finished basement, because the main public area's gigantic, yes, but also entirely open.
It's also very nice to be able to contain messes. So nice. One large shared living space plus kids means no part of your house ever doesn't look like shit without heroic efforts or paid help.