Why is it not possible to deploy for iOS on Windows?

I found many questions regarding whether it’s possible to deploy for iOS on Windows, and I know the answer is ‘No’. But I didn’t find any explanation on why this feature is not available?

When developing AIR for iOS applications using Flash or FlashBuilder, it’s perfectly possible to deploy for iOS from Windows. So, if Flash can do it, what’s the reason that Unity cannot?

Unity builds the project through Xcode - Xcode is only available on Mac.