Links to source articles below.
Yesterday 30 million users signed up for threads, which is already more than active users in the fediverse.
Furthermore, it seems that Meta hasn't launched threads in the EU due to uncertainty regarding the Digital Markets Act. It is entirely possible that their intent to federate with other Activitypub instances is entirely a cheap way to avoid being labeled a gatekeeper and avoid other regulatory requirements or restrictions.
It's future use of ActivityPub to get better publicity or scrape a bit more data might be an added benefit but not it's true purpose.
We'll see if launch in the EU goes hand in hand with them turning on Federation. I suspect that ActivityPub and the Fediverse are merely an afterthought to them and a convenient way to avoid being impacted by certain regulations.
Edit: Found a brief overview of the DMA. Among other things they say:
"The DMA aims to ensure the interoperability of messaging services allowing users on services like WhatsApp to send messages to users on smaller services like Signal"
https://ec.europa.eu/commission/presscorner/detail/en/ip_22_6423
Microsoft did this with browsers.
HTML was a thing, that was implemented by other browsers at the time. Netscape Navigator (the precursor to Firefox) was a thing that already did HTML well. It could access the world wide web, and was the defacto standard.
Microsoft introduced internet explorer, bundled with Windows. At first, internet explorer was not as good/complete/compatible as Netscape Navigator. Over time, it got better almost to parity. But it also added new features, features not in the HTML specification. They were not added to the specification, and how IE would use those features was not made public. So Netscape could not implement them.
Users started to expect those features.
Over time, more webpages would break on Netscape than on IE. Web designers wanted the fancy new features of ie. So users moved away from Netscape.
If only a number of technical users care about something, that the "mainstream" (for want of a better word) doesn't care about. Then things work less and less for the techies.
Meta could do the same with the Fediverse. As they already have market domination in other markets, they can introduce a lot of users to our "safe space". But be real if posts stop working and you as a techie knows it's because Meta have done something funky, Grandbob Jim isn't likely to care. Grandbob Jim will continue to use what "works". And some of the less techie of us will be forced to move to the MetaFediVerse to talk to our Grandbobs.
Thank you for explaining a real instance of this happening much better than I could.