Casual Twitter users who left twitter after Musk took over but aren't thinking all that hard about what it was specifically that Musk brings to the table that creates the problems. They just see someone else made a Twitter alike, and they already have an Instagram account, so they give it a shot.
All they know is the people they liked on twitter are gone, but that there were elements of the Twitter experience they liked
It would benefit a social cause that is near and dear to his heart: making Mark Zuckerberg extremely wealthy