Whether he does or doesn't is totally irrelevant to me. I'm not sure Gates ever cared for smartphones at all. At least, not the way they've evolved to this point. I concur with
@slooksterpsv in that smartphones were originally meant to be a marriage of a phone and a PDA and were not intended for consumption by the masses. All the credit goes to Steve Jobs' vision of getting them out there for all the world to enjoy. I don't think John Chen uses a BlackBerry and it's been known that Larry Page and Eric Schmidt used legacy BlackBerrys. What does that say about their belief in their respective products? Not a thing.
As long as shareholders are happy with the money flowing in I doubt they care what their CEO uses. It seems users of the platform care more about it than anyone else and
personally, I find that amusing. If Tim Cook announced he was going to ditch iPhones and use a Passport or go with a Sailfish OS phone, would you stop using your iPhone? Would you even care?
I have a Microsoft account, a Google account and an Apple ID. I can go to whichever platform I want and my app purchases will follow. Whatever is the best fit for me is what I go with, not what the CEO uses. I think I speak for a lot of us in the same situation.