#2 Timing

It's all about timing and there are several reasons why the timing is perfect for Ronda Rousey to lose the Women's title at the Royal Rumble. Not only is that evident by the Royal Rumble being one of the biggest pay per views of the year and a great place to crown a new champion, it also helps set up a plethora of matches in the meantime.
Think about it! WWE only has a few pay per views to go before WrestleMania 35 later this year and the best place to establish a new champion heading into the big event would be at The Royal Rumble. At least that way, it would be a big accomplishment for Bank's career and instantly establishes her credibility as she heads into WrestleMania as champion.
Look who just shut down all of Tony Khan's critics! More HERE.
Of course, WWE could always choose to do the title change at another pay per view or even on Monday Night Raw if they absolutely wanting to, but one would have to wonder if the moment would have anywhere near the same impact. One also has to wonder if WWE could find another suitable opponent for Rousey on Raw, which could be difficult given the current crop of unproven talent.
With that being said, the Royal Rumble just seems like the perfect time to crown Sasha Banks as champion and take the title away from Ronda Rousey. Again, it's also a great way to kick off the road to WrestleMania and build up a lot of suspense along the way, which is another reason why this is the perfect time to do it!