I imagine it like a casino acquiring a former-joke product, which made hologram/animatronic illusions of people "winning big" at a table or slot-machine. Now whenever they detect a current customer might cut their losses and go home--OMG, look, that person over there just hit the jackpot!
In other words, Facebook has a strong financial incentive to misrepresent (to ad-viewing customers, if not to investors) exactly how much social-ness is present to experience, and how much approval and attention the user gets from participating.
Soon everything will be The Truman Show.
But they could implement it without buying Moltbook. Easily. They have the money and the engineers to make it happen a hundred times over. Something like it already might be on Facebook.
To me, this feels more like acquiring the name. Everyone's heard that 'trademark' so they want to have it so they could reuse it for whatever they make later.