Like it happened with the other expensive mounts that still cost around 5 million credits? :P
Speaking of nosedive, the Progenitor had a Bantha for 5,5 million creds in the GTN today, I fully expect them to go down further.
My guess is those mounts that are still sitting around 5 mill + are ones from old packs you can no longer obtain otherwise. Good chance those ones will just go up more and more in price. The Bantha on the other hand is from a brand new pack, which will be available for who knows 3-6 months? New stuff always starts high. Give it a week I bet they will be under 1 million.