I really think they are not, those are all account from people who have actively signed up. Threads really is that much bigger than Mastodon, and it’s not that surprising.

People left reddit because reddit started charging for data access, and not the same people say they don’t want others to have access to their public data.

I can write a Mastodon scraper in a few minutes, make it scalable in a few days. Definitely easier than implementing ActivityPub in an app.

They can Scrape that data withiut federating. And I suspect once they federate Threads, Mastodon will be a tiny share of the resulting fediverse.

No to say they won’t ingest all that data, of course, they’ll get their hands on everything they can, but I doubt it’s the primary motivation behind it.