I think you're missing something important in this analysis: Awareness of the cycle and outside interference.
I'm one of the first people to bail when a platform or service becomes unusable and a new one becomes viable. I have zero loyalty: I started out in Usenet servers and with individual webpages and moved through to blogs/forums, then to Myspace and LiveJournal, and so on. (Including the Digg to Reddit migration).
This option is less available to me now because most new platforms are either bought out (Instagram) or require such high costs due to having to support multimedia bandwidth that there's nowhere for us to go. I'm not happy with the current platform options and I monitor them for meta-discussion fairly frequently and there is a portion of the Reddit and Twitter userbase that is ready to move IF something suitable comes along.
However, my desire for a new platform is directly at odds with the interests of the current companies and, unlike in the Myspace era, Zuck + the people running Reddit are aware of platform death and use their resources to keep their platforms 'alive' as long as they can. This is also why we see things like Instagram Reels and RPAN: The execs of social media companies know about platform death and manage for it. Think of Google's strategizing for the future versus Yahoo's: It's not that platform death can't happen, it's that they've been the ones sliding in that dagger so they want to defend against it.
It's like saying that calvary are irrelevant because somebody came up with anti-calvary tactics and strategies.
We're in this weird situation where those of us who like to explore new social frontiers and build new communities are only being given places to do so that either a.) Have strict social requirements already built in and that just kills our drive to see what happens if we put humans HERE and have them interact like THIS or b.) Are controlled by corporations who want to use that for their own benefit, and I'm NOT teaching, encouraging, or leading any more people to things I think will hurt or exploit them.
It's weird.