I was reading This Thread on the Achievement Forum, And curious as to why as well why there is no achievement being added for collecting 450 mounts as well.
Most of the mount achievements for collecting lots of mounts have been for every 50 mounts obtained on your characters! So I’m unsure as to why a 450 collected achieve isn’t being added, While the 500 one is.
If a 450 achievement is indeed added, I would love if we got a cool looking flying mount like stated in the thread I linked! 