There is a known strategy called EEE (Embrace, extend, and extinguish).
First, they embrace the open web. Millions of people who never would’ve joined the Fediverse (and, probably, don’t even know what the Fediverse is) flock to Threads and start to interact with us.
Then, they extend the open web, adding features to Threads that aren’t compatible with our servers. People on Threads don’t understand what’s wrong with our server (even though it’s Threads that’s the source of incompatibility).
Finally, they decide they’re “having trouble maintaining compatibility with third party servers” and start to break off from us, leaving us with no way to interact with our new friends. Unless, of course, we make a free Threads account…
Google Talk is perhaps the most relevant example of this. Here’s more details.