The news that Facebook's Android app has been collecting call and text histories is yet another black eye for the social media giant. But just why was Facebook able to siphon off records of who its users were contacting — and when — in the first place?

The short answer: Because Google let it. The longer answer: Well, it's complicated.

The social network acknowledged on Sunday that it began uploading call and text logs from phones running Google's Android system in 2015 — first via its Messenger app and later through an option in Facebook Lite, a stripped-down version of its main app. Facebook...