Though I'm not certain, my guess is Reddit is calling everyone's bluff; they've run the numbers and know that the long game is in their favor if they Tiktokify. Every social media platform eventually declines, and they must know that they have to adapt-or-die to maintain a similar rate of growth.
If there was a clear successor existing with a team that could scale fast, there wouldn't be a Reddit strike but a Reddit exodus. Lemmy and other garbage is not it...
How hard would it be to make a thing with the same API as Reddit so the apps that are currently about to shut down can instead change base domain and keep going?
Including existing OSS servers, assuming there already is some (complete!) open source one somewhere — I can google for the attempts ("plebbit" was submitted here for discussion only last week) but I can't trivially tell if they're any good.
Probably not hard to write an adapter at all. But it's not the API that made these apps popular and appealing. It's the Reddit community. The apps would write their own adapters if there was an alternative social media website with this community.
But the question is if people will willingly remain on a Reddit which is just like Tiktok or YT shorts or Instagram, etc and has no differentiator
Especially with their lousy mobile experience