It mostly comes down to Microsoft's mistakes.
Microsoft shattered people's trust with their DRM policies. It doesn't matter if they reversed it. The damage was already done. This, combined with a whopping 2 games (Only 1 of them exclusive) announced at the launch event, with the rest of the time spent talking about TV and other non-game features, caused the Xbox One to earn an image as an anti-games console.
And we all remember Sony's 2013 E3. That pretty much cemented Sony's PS4 as the go-to console for gamers. Everyone bought PS4's meaning their friends bought PS4's as well. Most people aren't loyal to a company, and are perfectly content with switching.
So TL;DR: Microsoft's mistakes, even though they reversed those mistakes, resulted in losing their customers' trust. People bought PS4's instead, causing a snowball effect of their friends buying more PS4's as well.
"Never argue with stupid people. They will drag you down to their level and then beat you with experience."
-Samuel Clemens
