It's easy to buy because that's the way wishful thinking is typically manipulated. Which is not to say that nobody can fantasize about her secret goodness or anything, but rather that it's exactly that instinct that her character draws on. We have adorable, 'sexy', and promises of power and fame. But if you notice how she bumps Sunset Shimmer halfway into the movie you can see she's doing it entirely for herself.
Of course, there are always reasons why someone turned out the way they did, but that's not exactly the point. In fact, I think the biggest point is that evilness (a word that actually applies for once!) and cuteness aren't mutually exclusive. ;D
It's easy to buy because that's the way wishful thinking is typically manipulated. Which is not to s