It may be that the industry has evolved to a degree that this is no longer viable (I also don’t know if I believe this…), but invite-only or otherwise limited launches formed the backbone of the current web.
Facebook was only available if you had a school address. Gmail was only available via invite. Obviously a service can’t stay in a limited state forever and the hype will run out, but it’s not exactly a new approach to limiting access early in the life of a service.
Google+ failed because Google killed it. I never experienced what you describe, but admittedly got an invite very early, and interacted with people who had also gotten the same thing.
Limiting onboarding does not eliminate the network. It just limits it. Again, to your point, this can’t last forever, but is not by itself the issue as long as they continue to scale up access. There are plenty of other issues that will make or break a network.
Bsky is the same; there's unexplainable pressure I feel in there to keep it to an in-group of nicest of people, but fine. It's not derailing into a Mastodon.
Someone please explain how a social network is supposed to succeed when it's invite-only? Hype alone won't carry it.
IMO, being invite-only is THE reason Google+ failed. There were so many memes about people getting excited for an invite, getting on, and then finding only a couple people they knew were on it, if any at all.
For a social network to work, it needs to be a network. Limiting on-boarding eliminates the network, and so people lose interest fast.