I agree with this. Maybe it doesn't apply to everyone, but I feel it can apply to most people.
For a while, I could have been described as "incel" (as in the literal description of the term, not the negative connotations it has picked up). I was not exactly popular with the ladies, and my dating history was close to nonexistent. My now wife was my first girlfriend and we met when I had pretty much thrown in the towel and given up on romantic relationships.
In an alternate version of my life I could have lived the single life and filled it with other activities and material possessions. I could imagine myself being happy to some extent living like that into my 30s, my 40s, maybe even early 50s. But after that?
Now I can't imagine life without her at my side.
I think there is a lot to be said for having a life partner that is beyond just a good friend and always has your back (yes I'm aware not all relationships/marriages are functional). Especially as the two of you grow older.
I feel the same about kids. We don't have immediate plans for kids. Right now we can imagine living without kids forever, but at the same time we also feel this will change and we'll regret not having one when we are in our 50s 60s or 70s, etc.