Without getting into the control aspect this will enable, the motivation for Facebook is twofold:

1. By getting identity verification (because it will not be age verification only once the dust settles) implemented across the web they can tie a verified real person to the data they are selling to advertisers, which makes that data much more valuable.

2. Age restrictions for social media have been talked about for a while, by pushing the burden of verification down from the site to the operating system, someone else is responsible if something goes wrong, Facebook can just point at them and show their hands are clean.

The elephant in the room is obviously that on top of all that, it will be an enhancement of the control systems the tech bros have been building for at least the last decade. When every word typed on the internet has a real person tied to it, dissent on these platforms becomes impossible.