iOS vs Android is a bit like ChromeOS vs Windows/MacOS/most Linux distros.

There are benefits to more restrictive operating systems. For example, iOS not allowing apps to run in the background essentially stops any apps with malware from doing stuff in the background, but it also stops apps like Briar, Syncthing, etc, from working well.

I assume Android isn't a problem for most Briar's users. They're likely running a deGoogled Android version (GrapheneOS, LineageOS, etc) and downloading/updating the app via F-Droid or something like that. They don't rely on Google (or Apple) to run anything.