Hi
Dubrovnik is one of the most beautiful cities in Europe,
However in this case for this trip making Dubrovnik at optional excursion, and switching it with another makes perfect sense. I wouldn't want to waste a whole day on a coach, and endure 2 border crossings (through Bosnia) each way to have only 1-2 hours in Dubrovnik, when I could be spending that time more doing something more interesting. I would have asked to remain behind. Now this switch has happened, this holiday has become more appealing, and better value for me as the national park is now included.
If Dubrovnik is the main attraction then there is a Dubrovnik and Dalmatian Coast tour, where you can get to spend much more time there.
Regards
Chris