#1 Sets up dream match between Rousey and Lynch

Let's be honest her - Ronda Rousey versus Becky Lynch is the match everyone wants to see at WrestleMania 35 and WWE most likely wants to start setting that up at the Royal Rumble pay per view. Of course how exactly WWE does this is still up in the air, but one would have to imagine that it would start with Lynch costing Rousey the title at the Royal Rumble.
With that being said and WWE seemingly working towards the aforementioned dream match at WrestleMania 35, it makes perfect sense for Rousey to lose the title to Banks at The Royal Rumble to set up the dream match. It also gives Lynch a chance to get her heat back after losing the Smackdown Live Women's title at TLC, which is another important plot point.
Look who just shut down all of Tony Khan's critics! More HERE.
In all honesty, Rousey losing the title in spectacular fashion at the Royal Rumble is the best way to go about this and really gives WWE the final piece of the puzzle that they need to set up Rousey versus Lynch at WrestleMania 35. Furthermore, it again gives the WWE Universe an OMG moment that will only serve to hook them on Lynch versus Rousey!