I agree on that score, and it is a bit of a likely unintended consequence of Dragonriding mounts in the Isles. I know from my experiences in the Beta, I've had zero call to use my other mounts outside of the Isles - and the "Favorite Mount" functionality that I tend to use prioritizes the Dragonriding mounts over all the rest, so unless I manually summon a mount it's going to be one of the small stable of eligible Dragonriding ones. This could of course change in future content patches in DF, especially if traditional flying opens up and all that, but at the start, the multitudes of my other mounts are going to just chill for the time being.