It prevents that specific strategy that would culminate in extinguishing. The idea being to siphon users away from other platforms, then add features that other platforms won't or can't implement, and use that to create an image of their own platform being better, having more features.
If they succeed at having a lot of users oblivious to what's happening, they will use those features, and when they don't work for people on other platforms, they will blame the other platforms instead of their own, further cultivating the image that other platforms are broken/unreliable.
In the end, they leave other platforms unable to compete, forcing users to either have a "broken"/incomplete experience, or migrate to their platforms. (Or leave the fediverse entirely). Or they can simply stop federating at that point, after users have left for their platform, cutting off the rest of the fediverse from content hosted on their platform.
The way defederating prevents a strategy like that is by cutting them off before they can get a foothold - they can't make users feel left out if they don't get to influence their experience in the first place.
Embrace: Join the fediverse with your existing user base that dwarfs the fediverse’s existing user base, and with infinitely more money.
Extend: Use your size, in terms of users and capital, to steer the direction of the ActivityPub fediverse standard to your advantage and your competitors’ disadvantage. You see everyone else as a competitor because you are a corporation seeking to monopolize the user base for profit.
Google is adding code to Chrome that will send tamper-proof information about your operating system and other software, and share it with websites. Google says this will reduce ad fraud. In practice, it reduces your control over your own computer, and is likely to mean that some websites will block access for everyone who's not using an "approved" operating system and browser. It also raises the barrier to entry for new browsers, something Google employees acknowledged in an unofficial explainer for the new feature, Web Environment Integrity (WEI).
I still stand by that defederation as the only line of defense is a losing strategy. Keeping users siloed in Facebook's garden shouldn't be seen as a win for us.
Keeping users siloed in Facebook’s garden shouldn’t be seen as a win for us.
Sometimes the only winning move is not to play. If people hadn't federated with google's XMPP back in the day, google wouldn't have had the same level of control it had to kill XMPP as a competitor.
We need to learn from the lessons of the past, and the past has resulted in the deaths of services when federating with corporations.