Facebook, Google, and other aggregators entice developers into using their APIs (or even their ad platforms). The developers get use of a nice analytics package

Facebook, Google, and other aggregators entice developers into using their APIs (or even their ad platforms). The developers get use of a nice analytics package, authentication, or other features, and in exchange Facebook and Google use those APIs to exfiltrate data from your device. They can tie all of this data neatly together using an identifier which Apple has to date provided as an opt-out service. Apple is now changing this to opt-in, so all these developers who have included APIs which are sneaking data out to the Google and Facebook will need to include a pop-up to get permissions to tie their data to the rest of Google and Facebook’s acquired knowledge about you.