I’m not the one who responded, just saying it’s pretty easy for someone to get the impression that you think someone stuck on a depressing treadmill might be sad.
It’s not the huge leap you seem to think it is from what you said.

“30 years on a treadmill and got nowhere” definitely has a negative connotation.

I think it’s just different people being in different places in their lives. For some people the stability and safety of the childhood home isn’t something they’ve replicated elsewhere yet, so the nostalgia is all they really have left of that feeling.

Even then they might not want to go back, but just be acutely feeling an absence of that type of security.

I’m sort of in the middle. I have a safe, stable and comfortable environment, and I’m doing my best to preserve that for my kids. I can also remember the feeling of childhood familiarity and just knowing how things will be, and not having the responsibility to keep that stability be mine. And that’s a comfortable blanket.
Not one I would want to live in, but having lost both my parents I do wish I could pull that blanket over my lap for a bit every once in a while.