#5 Lack of quality opponents
A lot of fans seem to still be upset that Nikki Bella was chosen as Ronda Rousey's opponent at Evolution, but those same fans fail to realize that the company doesn't exactly have many other options. In fact, beyond maybe Natalya, and Ember Moon, WWE has no one they can really stick in this high profile spot, which is probably why Bella was chosen
Of course, WWE could have always done a rematch from a previous title bout or even stack the deck against Rousey with a triple threat or fatal four-way situation, but that seems a little excessive right now. Furthermore, the storyline WWE is using with Rousey and Nikki has been very effective so far, which may have not been the case if another opponent was chosen.
In the end, this isn't a knock against any of the women on The Raw roster and just an example of no one really having the main event appeal to take on Rousey. Beyond that, doing this would have also forced WWE to decide between giving a young star a main event loss or having them go over Rousey, which could hurt her momentum.