Once upon a time, Android had a mail client that was part of the open source components. There was also GMail app that was closed source. Then a couple of versions later, the open source email app was discontinued and its functionality was incorporated into GMail. And the same thing has happened to many more apps and functionalities.
The F-Droid store provides compelling alternatives to essentially all of the old AOSP apps. (LineageOS also maintains varieties of them.) The one component where there's been a real issue for FLOSS apps is support for centralized push notifications, and that's reliant on 3rd-party services so "open" is not a very meaningful characterization anyway.
Part of that has more to do with the fact that AOSP is not used nearly as much and updating the default AOSP apps is not a good use of time for Google. The AOSP browser was never [edit: not recently] competitive with Chrome and the AOSP mail app was never [edit: not recently] competitive with Gmail.
> The AOSP browser was never competitive with Chrome
That's really not true, and not how it worked. Chrome was very late to the mobile game (first released 2012, a year after Android 4.0 / ICS was released) and its first few attempts on Android sucked. It was incredibly slow & laggy when it first finally came to Android.
It's obviously not a good use of resources to make two webkit-based browsers both targeting the same market, but it was a complete swap out from one to the other over a relatively short time-frame. It's not like the mail vs. gmail situation where it was actually two "competing" apps for quite a long while.
