Not sure what the timeline on that is, but the University of Washington had housing specifically for PhD students with families in the 60s/70s IIRC

Yes, a lot of public universities have had them. My knowledge of them at the two places I'm familiar with is that they're being phased out. One of them they were literally slated for demolition to make room for some other facilities (sport facilities I think) and another is still there but they opened up to other students and I think there was discussion of replacing them too, although they're still there as far as I know.

My overall sense of universities is that, like a lot of places, they increasingly see people as disposable and don't invest in them as much unless they're unusually financially profitable. Student housing is probably a bit different because people are marrying and having kids at older ages, but in the cases I know of the housing and housing cooperatives were still being used and liked. The subtext of discussions that I recall was that this wasn't enough, that the land needs to be put to use making more money for the university rather than supporting graduate students.

By relatively new, I meant "within the last 100 or so years." Princeton only ceased being a Presbyterian school in 1920. Certainly some graduates went on to other things before then, but the old model goes back hundreds of years.