#2 The match wasn't very exciting
There's only so much one can do in a match if you're selling a leg. Charlotte Flair attacked the leg and Becky Lynch sold it the best that she could, making it a very unexciting contest. On a night filled with multi-man fast-paced matches, this was a definite low point because of the story it told.
And therefore, it needed Ronda Rousey's interference to make the match actually memorable. If not, it would have been a by the numbers match that ends with a lucky roll up victory for Becky Lynch. Plus, Ronda Rousey's interference creates a massive talking point for WWE RAW this week.
We've seen Charlotte Flair and Becky Lynch tear it up in the past when given the opportunity, most recently at Evolution, and so we know that it wasn't because of a lack of talent that they didn't deliver a barn burner. It was the plan all along.