I think Twitter is unique in the fact that it's more driven as a news feed/update app than a social conversation app. Most people go there for news. If it didn't have the immediate and direct news update aspect of it, it never would have become a thing in the first place and never would have taken off.
So even when the invite only on Bluesky ends and regular users can go over there, unless major news organizations and news people like entertainment, politics, sports, science, etc all go over there, then no one will actually leave Twitter because that's where they'll get all their news feeds from.
What would change the game is if say the major networks news feeds cancelled their Twitter accounts and went over to Bluesky or some major sports news accounts or entertainment news accounts or celebrities cancelled their Twitter accounts and went over there. But I don't see that happening, because the big accounts won't leave the big user base. Lady Gaga, Taylor Swift, Adam Schefter, and CNN, etc won't go exclusively to a platform that doesn't have enough eyeballs on their content.
I think Bluesky would have to generate hundreds of millions of users for those major news accounts to even consider leaving and most users won't consider leaving unless those major accounts are already on Bluesky. So it's kind of like a catch 22.