It seems like it would be simple enough, but it's death by a thousand cuts. Supporting Android means having to keep track of even more screen sizes, OS versions, updates, app store releases and so on. It just adds on more and more. For one developer who is trying to prove out an idea, the work to support the app on multiple platforms just eats up your time and focus when you really should be focusing on features and adjusting what the product is as you get more info from your existing customers.
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.
