"It's not the who, but the why, that matters." Oh really? [FINALE SPOILERS]

I will preface this by saying that I did not have an A theory. I wanted to be surprised, and I didn't want to have my hopes and dreams dashed if my theory didn't materialize. I am not bitter because "I lost," because I didn't have a dog in the fight.

Moreover, I think CeCe is a fine, logical A. There was so much evidence for her that she had to have been involved. Which is part of why I'm so disappointed -- there was no shock factor. If anything, she would have been a great candidate for Red Coat. All the evidence was there for her involvement, but there weren't all the messy plotholes (including dating her own brother, which I'm still not over).

But here's my big problem. We were told over and over that the who didn't matter but the why was super important. And yet, while I'm OK with the who, I'm completely flabbergasted by the why. Unless I missed something, the two major reasons provided were:

• CeCe heard about "the game" from Mona, and it seemed so irresistible that she ruined multiple people's lives over it.
• CeCe thought that the Liars were happy Ali was gone (which wasn't even really true...it's like she was thinking of Sara's friends), and that "really pissed [her] off."

If CeCe (formerly known as Charles) had made it her life's mission to punish Mr. DiLaurentis for what he did, then she'd have a really justifiable why. But instead, she went after mostly innocent people for fun. Am I missing something?