MS has almost always had customizable toolbars, floaty-undockable, multiple toolbars and drop down menu's that hide unused features.
Vs. the Ribbons: Hide/Display and can't change.
If you try and make a custom Ribbon, you can't accomplish the same layout due to placement and sizing restrictions.
Performing an action via Toolbar or Drop-Down menu, doesn't change your menus or interface. Whereas the Ribbon requires - changing to a "specialty" ribbon, finding said function on the ribbon, clicking, changing back to "Home".
Conceptually the ribbon is good, but when it's implementation comes with the complete removal of previous functionality it completely goes against the flexibility that we've become accustomed to over the years, and feels like a slap in the face.