I don't find any reason to repetitively check a post on Facebook (or Instagram / any of the other image/video sharing platforms.) If I put something up, I can go back and find out what my "final earnings" in social-capital were days/weeks later. There's no
urgency to that. It's not like the stock market; it's not going to suddenly start dropping. It just rises until it plateaus.
I find places where I leave comments (like Reddit, or HN, but Twitter also works this way) a lot worse for this "addiction via narcissism" aspect. On these services, your post/comment doesn't only get more and more popular; it may also be rebutted by a reply (not necessarily made in good faith), at which point it might start getting less popular, possibly dipping into the negatives if the reply's reinterpretation paints you in a bad-enough light. Because of this, there's a feeling of having to watch for these replies, and leap to defend your post against them, so that the reply's interpretation of your words doesn't "win out" against your own actual meaning (which may not always have been perfectly clear from your original, succinct wording.)
That's "narcissism" too, in a much stronger sense of what Narcissistic Personality Disorder means: the obsessive paranoia over losing social capital, due to being perceived as having committed a social faux-pas, that leads one to avoid taking social risks, and perhaps even lying to make oneself seem more "middle-of-the-road" within one's social cluster than one actually is in private.