I'm (and my friends) are in our 40's-50's.
We have our children, or not, but more importantly, our pension and own homes, which we don't need to have our Partners living in.
I think that this is becoming more common, in the generation hitting their 40's+.
Whereas you might want to live together when you are younger, once you reach a level of Independance, or have teenagers still at home, you shy away from living together.
In my last relationship, we took every Holliday together and was together most nights. Even at our busiest, we made time for each other.
Our six year relationship, included the death and disability of relatives, hospital stays, redundancy etc.
We were committed and in a Partnership, more so than some of the married couples I know.
We could rely on each other.
I don't want to live with someone ever again, tbh, but I would enter into another Partnership, or date.