What do you mean? There's plenty of examples on Android where users have been tricked into sideloading malicious apps.

You just said there would be "five different App Stores", yet this hasn't happened on Android.

Amazon has an app store for Android, but its apps are all on the Google Play Store. It's really there to serve Amazon's Fire platform where Amazon doesn't licence Google Play.

Samsung has an app store for Android, but again, all of its apps it makes available to other non-Samsung device users are on Google Play.

Additional app stores on Android have so far been complementary to Google Play, which remains the place where the overwhelming majority of apps are obtained.