Because you are making a "Video DVD"

And that is a standard carved in stone. You want a Video DVD but without bars on a HD WideScreen. This will never happen because these two standards don't support such.

If you were to create some other type DVD and play it on some of the better BluRay players you might fix that but I can't write what it takes here. I'll just leave with a search about that.
https://www.google.com/search?as_q=How+to+make+a+HD+DVD

Bob