why do you think most business are already writing a separate Android app

I don't think that. I know some businesses who are still writing separate apps, instead of switching to cross-platform. You'll have to ask them why they're doing that. It frustrates me no end when platform-specific bugs come up because they're running different code on each platform, each written by different people.

the fact that people interact by touch rather than with a mouse and keyboard

...makes no difference at all. Whether a user has touched a button, clicked on it, or tabbed to it and pressed enter, the same Button.Clicked event gets triggered.