Every now and then, something happens that Twilight feels the need to question. Why didn't Celestia tell her about the Elements, when she asked before Nightmare Moon's return? Why does Ponyville allow pegasus or earth pony magic during Winter Wrap-up, but not unicorn magic? Why were there no stallions at the Running of the Leaves?

And, like any good student, when Twilight finds a need to ask a question, she asks it.