testflight have max 100 internal testers and 10000 external testers. So if we assume that they use the internal test system for ios. Androis also have a limit to 100 internal testers and closed test i think is unlimited.
Anyhow if we assume that they have 100 beta testers on both android and ios i would guess that most of them doesn't report back to zwo. Many of the small bugs and quirks should then have been discovered before a public release. Or maybe the beta users is relatively newly introduced.
Its a good idea to have relatively many beta testers but only if all of them actually report back. Getting beta tester status just to get software before every one else is ok but the majority should be active and report back bugs and suggestions for improvements. If not all the users that are not beta testers get to enjoy all the bugs that should have been discovered.
Don't get me wrong i'm not pointing at any one but my own experience as a developer for both android/ios i had several beta testers that did not report back and apps was published with bugs that should never happen.
To few testers can give this result but also to many.
Anyhow i would like to be a beta tester as im relatively systematic in trying to find bugs in software. But my experience with astrophoto and also the fact that the weather here is almost cloudy all year (feels like that). Then i don't have enough clear sky to be an active beta tester.
For those who are beta testers i hope you have lotz of clear sky and try to do thing that the developers doesn't expect so that they can fix it. And also give feedback on improvements. Then we all gain on this :-)