User accounts are stored server side, there is nothing to remove from the device during an uninstall of the app.

The accounts are filled in when the device opens by a web request to the mobile application server, not from a local data store. Part of the request is the device ID which is physically part of the device, not the application installed on the device. Whenever the app opens it makes a call to the server to retrieve accounts; none of this data is local to the mobile device and can only be deleted through the app. If the accounts are deleted prior to the uninstall, they will not show up upon reinstall.