If you read the NYT article, there's one pretty obvious reason why they can get away with ending the partnerships now: almost everyone has smartphones that can just run the official Facebook app. It probably also helps to understand that on a few of the older platforms, almost everything went through the manufacturer's servers, including email and sometimes even web browsing.
While I guess technically they could've use the normal API and only got the same information as Farmville or any random quiz could, this would have the result that - depending on what phones your friends used - you wouldn't be able to share information with all your friends without also sharing it with Farmville, Cambridge Analytica, and all the other shady Facebook platform apps that weren't held to the same privacy standards. That doesn't seem like a win to me, particularly since getting someone to click "yes" on a permissions dialog is a lot easier than creating a widely-used hardware platform and convincing them to use it.
(Of course, given just how many intrusive permissions it demands, getting everyone on the official Facebook app arguably isn't a great leap forward for privacy either.)
While I guess technically they could've use the normal API and only got the same information as Farmville or any random quiz could, this would have the result that - depending on what phones your friends used - you wouldn't be able to share information with all your friends without also sharing it with Farmville, Cambridge Analytica, and all the other shady Facebook platform apps that weren't held to the same privacy standards. That doesn't seem like a win to me, particularly since getting someone to click "yes" on a permissions dialog is a lot easier than creating a widely-used hardware platform and convincing them to use it.
(Of course, given just how many intrusive permissions it demands, getting everyone on the official Facebook app arguably isn't a great leap forward for privacy either.)