It's not just leftists. My Twitter feed had a large number of military experts in it since the start of the war against Ukraine. Almost all of them are posting on Bluesky now, and they're certainly not a leftwing group.

I think another interesting aspect is that Musk confirmed that tweets with links to external sources are penalized on Twitter. That would particularly hit the kind of people that make these platforms interesting to me because they also post longer content somewhere else.