Exactly this, the only real reason that Meta would care about the rest of the Fediverse is free extra content for their users and extra data to exploit
Defederating doesn't stop either one of these things, content is still viewable (defederating only stops other users on other instances being able to comment, vote etc) and the data is still their for the taking
It feels like half the posts/comments at the moment don't understand the way that defederating works
Defederating won't do jack shit to meta, they can still view your content and view data to their hearts content
All defederating does is stop you within your instance being able to see posts from Threads
The two things Meta likely cares about is content and data, both of which they can still get