#1. To set up a major heel run in the future
We all know the rumours that Ronda Rousey's run in WWE this time probably won't last past WrestleMania 35. The reason for this is because of her desire to start a family. If that is the case, it means that she'll be off TV for over a year at the very least.
Not that she'll be retired for good, but she could still come back and make part-time apperances as well. With Rousey, there's so much potential that's yet to be tapped, and with a heel turn, WWE may already be setting up future plans for her.
Rousey could have an epic heel run at some point in the future, going on a dominant monster run. By then, we're sure that the Shafir and Duke will be ready as well, and the Four Horsewomen vs Four Horsewomen feud could eventually happen.