Until that happens, it would be a huge waste of time and money for the developer to build an Android version, since it too would fail as a product, just like the iOS version.
Multiplying 0 by 2 is still 0.
The situation might be different for an app whose success depended on the user's ability to use the app to communicate with all of their friends, some of which had Android phones.
There are of course frameworks out there to help you build one codebase for multiple platforms, but if you go down that route, if you aren't familiar with the framework, you have to learn it. There are going to be quirks in them that you're not aware of. Maybe framework version X only works with iOS version Y and Android version Z. It just goes on and on. Frameworks aren't perfect either, and things don't work exactly the same across platforms even with the framework.
Think Clubhouse only moving to android when it was working on iOS.