On Android today, third party password managers are forced to integrate with Chrome using custom keyboard (IMEs) or accessibility services. These are well known vectors for abuse on Android, specifically when using work profiles to segregate enterprise data.
If Chrome for Android were to integrate with AFF to support autofill from third party password managers, Google and Android Enterprise customers would be able to enforce stricter policies over which apps can act as an IME or accessibility service.
Comment 1 by zkoch@chromium.org
, Jun 7 2018