If I was selling my software at Walmart, I have to change nothing to sell it at Target.
You don't have that choice in iOS.
Over upcoming releases of AOSP, Google intends to disable sideloading in Android, except for that tiny tech audience who knows how to enable developer mode and install over the command line. So, both direct APK downloads and F-Droid will be accessible to fewer ordinary Android users than is already the case. Definitely not enough people to build an app business on.
https://www.androidpolice.com/2020/08/24/android-11-install-...
This is a gross and anti-competitive overstep.
With android, I can have an .apk that is distributed via the play store or I can have that exact same .apk distributed via any other store that exists for that device.