He/she is probably a pretty different person than the one you married. It's easy to overlook that.
I'd say this is also valuable advice for yourself; what are your current dreams? Do you really still want all of the books on your bookshelf? Where do you want to go? Who of your friends haven't you seen, but need to? I find I don't spend enough time on that for myself.
Source: married for 30 years and practicing this since we found out we needed to after years of ignorance.
Easy to glean the high level techniques in an hour. eg avoiding the Four Horsemen of relationship killers. But I've been working on my technique for years and feel like I'm just getting started.
But I think the poster's point was that this advice is basically advice for long-term relationships and really shouldn't be viewed under the light of marriage only. Since many folks don't have to be married to be a family, a good number of folks are skipping that step.
Don't get me wrong, we talk about it. If one of us has thoughts about it, we share at the time or soon after. But it isn't like we lead busy lives or have children or in general, have a lot of upheaval in our lives. We are both over 40, and aren't changing rapidly at this point. There simply isn't that much to discuss.