While this mechanic makes sense in PvP modes, in the PvE overlands it acts as nothing more than an annoyance that takes away player agency. It's especially annoying when you move by something, the mount despawns in shallow water and then can't mount due to a lowly scrib chasing you a mile back. In close proximity with enemies, you can already be thrown off your mount if it's depleted of stamina upon taking damage, this serves a similar purpose while only happening within close proximity with mobs.