You said a need to "rewrite". That is simply not true. With C++/Qt I've only need to compile without changing a single line of code in any platform.

So you are arguing that no one "would say re-writing the same app 5 times and maintaining 5 codebases is a bad idea."?

That was my statement. You are saying it's not true. All the upvotes suggest some would say that. Therefore my statement is true.

I'm not sure why you're so confused here. This isn't at all applicable to what you are saying. You are talking about writing an app once and having one code base, which is exactly the opposite of what I was talking about. You have constructed a straw man and called it not true.