Why MS scrapped the menu.
As I understand, MS frequently received requests asking for features to be added to the Office apps. The problem was that many of the requested features were already present; users just couldn't find them.
The Ribbon is an attempt to rearrange the menus to make more visible those features most frequently used or asked about. That obviously is going to result in making some features less visible. One's opinion of their degree of success will be influenced by the number of one's favorite features that were affected.