It’s about control. If it’s my data, I should be able to give permission for other apps to access it - regardless of whether Facebook views them as a competitor. Likewise, I should be able to block access for a given third party - regardless of how much money such a “partnership” would generate for Facebook.

So yes, it is anti-competitive for Facebook to block access against the explicit wishes of its users. But it’s also despicable to sell user data to whomever without asking permission first. It’s pretty obvious from Facebook’s actions that they consider it their data, not your data.