OK, fair point, it's an inexact example. I suppose my point was that originally, “Android” was mostly open source. Google then quietly replaced parts with prop

OK, fair point, it's an inexact example. I suppose my point was that originally, “Android” was mostly open source. Google then quietly replaced parts with proprietary equivalents with a few more features, and now AOSP is nowhere near as useful (to ordinary consumers) as Google's proprietary distribution of Android. A similar story could happen to a proprietary fork of a permissively-licensed open source project. Copyleft licences are designed to prevent proprietary forks. And of course if you don't want that, you can license your code using a permissive licence. But that's why someone might choose a copyleft licence.