There must never be a single dominant instance. If one instance becomes too large, they end up having too much influential power. And with all that power, big corporations or power tripping admins will use that power to coerce other instances to do certain things. "Don't want to follow our unilaterally-imposed rule? We're gonna cut off your entire instance and your users will lose access to our communities."
If Meta doesn't get defederated, they will become the dominant instance. They already have the most amount of users since I'm assuming you can use your Facebook/Instagram account, they'll have the most amount of user activity, and of course the most amount of power.
For me, it's more like "Did I accidentally drop a hot take and got the entire community to go against me?"