Ironically this is how night clubs work, too. One gets a monopoly/gets popular and everyone goes there for a time until it because uncool and people move on to the next cool club. In social media see LiveJournal -> MySpace -> Facebook -> Tiktok. Each had a monopoly at the time until something cooler came along. The tenure also, ironically, seems to be around the same duration of a popular nightclub.
Also, don't mistake user bases for monoliths in this analogy, < 18 moved on from facebook a long time ago, > 50 may skip Tiktok entirely but they showed up years after ~18 year olds did so tenure is still relevant.
This is not a good take. First, it's not true that the most popular club has a monopoly in any meaningful sense. But even granting you that farcical premise: any "monopoly" effect is on a city-wide basis and does not scale, and does not trend towards global winner-take-all outcomes that social media does.
I'm not sure which night clubs you are going to, but "popular" ones are very much monopolies. Sure, the local bar that plays music isn't a monopoly, but neither is the "small" social network. You won't see John Mayer in a small night club and you also wont see him on a small social media platform. John creates lock-in for the other high status participants at the club, just like the content creators create lock-in for you being on social media (or HN in this case). I can walk next door, but I have a worse experience in both cases because they have a monopoly over a network is valuable.
Your second point of the global nature misses the point I was making. Social things evolve. Whether on a global scale, country scale, or city level. Assuming there is a social construct that will "just work" until the end of time seems naive. But hey, if we are all using Twitter and Facebook in 20-30 years rather than the new social media company that has come to prominence then it will be a provably wrong take :).
Or maybe a better way to put it is if the next generation is using them, because certain cohorts (see original post) will continue to use it because thats where their network is, but younger people get no utility because their network isnt there. See twitter and facebook.
