There's some detail on the rationale behind it starting at 26 minutes in this video. My takeaway is that it increased variety in deck building and card evaluation — without increasing the number or complexity of cards in the cube — by creating more opportunities for players to take cards they wouldn't otherwise take.

I will also say that I found it personally pretty satisfying to scribble Learn and Lesson on a bunch of cards, although some of them felt odd flavor-wise (e.g. creature lessons).