- Exploring. Finding places where you can not go by foot. There are sooo many beautiful places that my friends and I have found over the years. Did you know that there's this lovely area north east of Moonglade that's just perfect for RP druid meetings?
- Enjoying the flying itself. Flying is one of these ultimate dreams of mankind. When you ask a given number of people what superpower they'd choose if they could have any, usually a majority of them will say "flying". (I personally wouldn't, I think there are far more useful super powers ) Just sitting on your flying mount and soaring above, choosing where to fly independently at any given second, seeing places from above that you've only known from below, in a whole new perspective ... it's magnificent.
Maybe this will explain it better than I can
Btw, I agree with you that exploring the world by foot is beautiful as well. Which is why everyone should do it, at the start of the expansion, while leveling. Get to know the continent by foot, and then rise above it and see "a whole new world", see all the places you knew before from a different perspective. Why limit yourself to only one of the two? Or more importantly, why would you want to limit other players to only one of the two?