During uninstall take them to a page where you very simply and sincerely ask them for feedback. Promise that you will read it and respond to it. Don’t require an email on that form though so they can answer anonymously if they want to.
Not sure what the timeframe is between a user trying it out and subsequently uninstalling, but if there is a bit of a time gap, the decreased interaction analytics could be a used as a leading indicator of pending uninstallation and used to trigger a win-back attempt?