#3 To unify the championships
This one is another major possibility, one that we sincerely hope isn't true. What bigger way would there be to end the show than by having one unified Women's Champion? After all, this is the women's championship match on the show, and it's to contest and see who the best woman on the roster is.
To do that, WWE may feel that they need a unified Women's champion, and this could be a reason why they're putting both titles on the line. Becky Lynch, if she wins, could walk into RAW with one unified championship.
However, we hope it isn't true because it could be seriously detrimental to the Women's division in the long run. Having the additional title most certainly helps the blue brand and helps push other women as well.
In UFC and boxing, every division has a title, so what's wrong with two brands having two separate titles?