The problem is, there’s just way too many things on the top bar. For example, you might want to print. How do you do it? Well, you could design a print icon in the top bar. But it’s probably not worth it. You could hide it in the ribbon, but that sort of sucks for discoverability.
And then you notice the top left corner. And you think “Well, tons of Android apps just put everything there. Maybe we could try that?”
And so it became clear, due to the massive number of features in Office apps, and the extremely tight real estate, and alignment with tablets, that a hamburger was the best overall pattern.
And Later:
I was out for coffee with a Windows PM a few weeks ago and she said “what do you think of the hamburger?” And I’m starting to piece 2+2 together. Apparently there’s a big hamburger backlash brewing in the Windows community that I wasn’t aware of.
But here’s a design challenge. And I’m serious – when Excel comes out, download it and see everything in the hamburger. Then redesign it. I’m curious to see what people come up with, because I’m always ready to see more ideas. We went through a ton but that doesn’t mean we could have thought of everything
There’s always more ideas, but sticking to conventions can save time for design work on other, possibly more complex or important problems. I’m confident a better pattern will evolve eventually, but it might not be as universal.