Ex-Microsoft Windows Phone designer explains the move to the Hamburger menu in Windows 10 Mobile

The move to the hamburger menu in Windows 10 Mobile has been incredibly controversial, with Windows Phone not just losing one handed usage, but also differentiation from other mobile operating systems.
An ex-Microsoft designer has now broken the silence on the move in a reddit AMA, and has revealed that the internal debate has been going on for at least 2 years now inside Microsoft.
The short version on why the company eventually settled on the hamburger menu, according to ex-Microsoft Interaction Designer Jon Bell is:

Hello! These are all super common questions. But let me unpack some of your statements and dissect them a bit.
*.Why not let the user swipe?
*.Hamburger – bottom is better if you interact a lot
1) Swiping sucks. It hides content. Let’s say you’re in Format and you want to get to something 5 tabs away. Five swipes is an unacceptable series of interactions. The carousel model has been disproven repeatedly, every single decade, for several decades. We have the data. It’s a dumb interaction model, full stop.
2) It turns out bottom is not better. You’d think that something 3 pixels from your palm would be easier to reach than something in the middle of the phone. But nope. The way average people hold phones means the middle of the device is the best location. Both bottom and top require your hand to make a bit of a shift to reach. (this is why swiping on items to get options like “flag message” or “delete” is popular. Make the gesture contextual to the item itself and you don’t make people reach to use it. And this is, again, why reserving swipe at the app level for navigation is not a good model.)
2b) You don’t use the hamburger very often. Most of your time is spent reading, and then some of your time is spent manipulating the content. So if we put the hamburger on the bottom (which no major app in the whole industry does) then the app bar on the bottom would have to get larger in Office. And in the case of Outlook, you’d have to actually put a bar down there in the first place.
2c) Once you have an app bar again, in order to put the hamburger, you’ll want to use that space. So maybe you put status down there. Maybe you put refresh. Maybe you put compose new. Well maybe you don’t need the top bar anymore!
2d) Except you do. So you know what folder you’re in. (and in other apps, what document you’re looking at, or whatever) So the choice is either “Align with the rest of the industry by putting the bar on the top with some key actions and a hamburger” or “Put chrome on the top and bottom” or “Lose the title bar at the top, putting it at odds with every mobile OS on the planet.”
They chose correctly.
Jon Bell goes on to note that there were  numerous other reasons, including aligning with other mobile operating systems and the ability to create universal apps which work on any screen size, and that the decision was supported by usability studies both internally and externally which showed that one-handed usage was not a significant priority for users, especially with larger and larger phones.
He notes that pivots hid options, saying “seeing half of the next pivot still does nothing to let you see the pivot that are three away.”

Probably controversially for Windows Phone fans, he notes:
This isn’t a popular opinion on this particular forum, but the interaction patterns in Android and iOS are better designed(at least compared to 7). You can disagree, you can say I’m a fanboy, whatever, I don’t mind.
But get into the labs and watch people use all three platforms. There’s data here that not everyone is privy to, but that doesn’t make it less true. There are some real weaknesses in the old Metro patterns.
But point taken. Maybe iOS and Android forced everyone to two handed use with shitty design. Which came first, the bad design or the coping strategies?
Well, in this case we have an answer. Big screens exploded in popularity. (I argued against big screens for a long time. I was 100% wrong.) By the time you say you’re ok being a tiny South Korean teenager with an eight inch phablet, the ship has sailed. You’re going two handed.
And again, as I’ve said elsewhere, the hamburger is for lesser used things. The most common usage pattern, by far, is scrolling through content and reading it. So as long as you can thumb around, you’re happy. All that other shit should be easy to use, but top left is much less of a problem than it sounds like it might be on paper.

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
He also noted:

The stark look of Windows Phone seemed to turn off more people than fell in love with it. I know here in this forum we’re all fans but in the mainstream marketing was only one problem. Apps was another. But the biggest one was lack of relevance. People didn’t understand why they should care. A lot of people said it looked like a nice phone, but it wasn’t for them.
He also revealed that Microsoft continues to work very hard on Windows Phone, despite the appearance of them de-emphasizing it.
The AMA is definitely worth a read and can be found here: http://bit.ly/1DuppFv
Source: WMPowerUser