I feel like the answer is not that hard... someone just needs to make a copy of the basic functionality of twitter with better intentions and not owned by Musk et al. If they are sufficiently trustworthy and competent in how they do it, I really believe that lots of people would be willing and even eager to jump ship immediately.
Mastodon and others tried to do this but they keep spending all this energy on decentralization which is not the problem to solve. The problem is just to be Twitter but (a) not shit, (b) trustworthy, and (c) prosocial. People want to move, just give them somewhere to go and demonstrate more empathy for them than twitter does (not hard).
Implementing this should not be too hard in the AI era and considering that a lot of people would probably donate engineering effort to a Twitter replacement. Paying for it is of course annoying, especially at scale but maybe that's solvable (ideally with a donation model / raising money from people who want to see it exist instead of taking outside investment, or at least limiting the influence of investors so you don't end up making Twitter again). Running it should be easy, just "try to do a good job" (I volunteer, but I don't even use Twitter so I'd probably not be a good candidate). Getting sued for patent violations or something might be a real problem, but maybe it's circumventable, I dunno.
It often feels like every knew large-scale project is corrupted by the Silicon valley funding model (yes I know I'm on a site that has a lot to d with that), so everyone has lost any trust that a new thing will ever be benevolent... but seriously it is not that hard to start a website, that's what Twitter and Reddit and all them did back in the day. The problem is aligning the site to people's morals enough that everybody hypes you up for free. Which ... I think things have gotten so bad now that one could get a lot of free labor if you even start moving in this direction and seem like a serious contender. Although all the VCs are trying to cash in, all the other 'normal' people really just want to live in a safe and happy world where institutions operate prosocially instead of the opposite, and they'll often do whatever they can to manifest that... if somebody just makes it easy to do.
You described Bluesky. They did get founded to pursue decentralization, but it's completely ignorable. It largely operated as a centralized service.
From my vantage point the decentralization stuff distracted them from winning, but I am too ignorant to be sure if that's valid or not.
The ideal twitter clone does, unfortunately, have to clone the "virality" aspect, including the recommendation algorithm, at least at first. A necessary evil, but at least it would be in better hands if it was rebuilt by more prosocial owners.
I agree that the focus on decentralization is a distraction, but Mastodon and Bluesky are perfectly fine alternatives that are just as easy to use as Twitter.
The fact that they have not succeeded in attracting a critical mass of Twitter users to jump ship is all the evidence we need to show that network effects are real, and overcoming them is really hard.
Also, I don't think most people on Twitter "want" to move. I think most people don't care about Musk or his politics, at least not enough to care about leaving his social media site. (And a significant chunk of people in the US, at least, likely are in Musk's camp anyway.)
> someone just needs to
You did the meme. ;) Literally billions of dollars are waiting for you, after you complete this simple task!
Problem is, what's stopping you? What stopping everyone else? Why did everyone that tried so far fail? If the answer to a billion dollar, highly public, problem is trivial, but nobody has done that trivial thing, then that entire aspect of the problem is not actually that important, or even a factor at all, as an http server, serving a cloned twitter is in this case!
I did it on purpose! In one sense it's really hard, of course, but in another it's simple, right? Simple enough that if a bunch of people who skim this a try plus their personal touches, I could easily imagine one of them succeeding.
As with many problems in the world... the first subproblem is that not many people many are very inspired to fight. Which is why it's important to emphasize its straightforwardness.