Can't apps start up the facebook SDK after someone has clicked the facebook login button? If someone has already logged in with facebook, set a flag in NSUserDefaults, and start the sdk then.
I'm pretty sure they can (though another comment states the opposite and might be right), and I'm definitely sure they can even implement the whole Facebook login through standard OAuth without using any of Facebook's code.
They choose not to because 1) it's easier and 2) Facebook gives them a "cut" of the revenue in the form of free analytics and insights into how their Facebook ads are performing.
The companies decided that the value they get out of Facebook ads & analytics are worth more than their customers' privacy. Until well-enforced regulations come into play (so not the GDPR) nothing will change.
