For apps that have been popular for a long time, I wonder if there is a negative bias in reviews (beyond that already present in all online reviews). A customer who gets an update that breaks an app they use every day is very likely to submit a negative review (even if they have reviewed positively in the past). However, a customer that gets and update that make incremental changes that largely don't affect them has no incentive to go post a positive review of the new version. So, the positive reviews come only from new customers, which are relatively small for apps that have reached saturation.

Messenger is much more intrusive to the whole phone experience than the Facebook messaging functionality that was included in the app. Though, to be honest, even that went downhill in the same direction as Messenger -- though not as far -- before it was removed and messenger made mandatory.

Many don't trust FB anymore or the invasive data tracking of Messenger. I've overheard comments from friends and family that they won't be forced to download another app, especially one that keeps such close watch on users.