#2 Because the WWE wanted to freshen things up

Lets be honest here, everyone loves to see mixed tag team matches in the WWE, irrespective of which wrestlers are battling in the ring. In my opinion, they are way better than the meaningless singles matches which take place between the lower card wrestlers on RAW every week.
To watch this mixed tag team match was way more entertaining than it would have been watching a match between Jinder Mahal and Apollo Crews, or Ember Moon and Alicia Fox.
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The McMahons had promised us a fresher product few weeks ago, and if you have noticed closely - the number of meaningless one-on-one matches have reduced by a considerable amount on WWE TV.
Also, it gives TV time to the lower card superstars of both the male and the female division, so to have mixed tag team matches is a good idea actually.