Your kid doesn’t need their own room. In fact, neither do you. Everyone could live so much more carbon efficiently if we accepted communal living. Like dorm rooms. People all around the world rent small apartments with their extended families, and sometimes even other families. The only reason people in the west believe they need a single family home is because they’re entitled and have a weird focus on individualism…
Or, they like having sex? I'm not having sex with my kid sleeping in the same room. And I'm not particularly interested in having to manage my sex life around my kids sleep schedule. I don't know why you think adults wanting a space they can do whatever they want without their kids witnessing the activity means they have a "weird focus on individualism".
I think whatever allows the parents to be happy and take the best care of their kids is ideal. If they need sex to stay close (very normal) then so be it. I think modeling a close and loving relationship is great for kids.
We co-slept with our kids and it was terrible for our sex life. I don’t regret it - the kids loved it and it made a lot of things easier, but I have a hard time imagining how you’d tackle the sex aspect without a great support network and flexible work - anything to allow more time alone here and there.