I haven't used office in a while, but I remember that once a function wasn't in the "home" ribbon, finding it required searching through the other sections. And the division of those sections was super counterintuitive for me. Whereas I could usually hazard a pretty good guess where something would be in the drop-downs.

Well I used to read a list of options horizontally, then click one and read a list of options vertically. Now, with the ribbon, I must observe a grid of different sized and shaped objects. That's harder to parse, in my opinion.