What's completely nonsensical is to act like there aren't any strings attached when there are obviously strings attached.
Let's look at the strings
Meta is trying to maximize profit. Anyone who thinks that Zuckerberg suddenly cares about an open fediverse even though its values (people being on multiple instances, everything being transparent, no one person or group having too much control, etc.) go directly against his goal is either delusional or very misinformed about what these for-profit tech companies do.
That's all true. But that's not really a string - it's just a fact of any for-profit organisation that sets up an instance
It strongly benefits him to take users from Mastodon, Firefish, Misskey, Kbin, etc., and allowing ourselves to depend on him for fediverse activity puts him in a prime position to do it.
But he can do that anyway. And in fact people who who want to interact with the 140million ish Threads users currently have one option - join Threads. With federation I can communicate with Threads users without joining Threads. That needs to be factored in.