It's no surprise really when they force the update on you, maybe not on all users but it happened to me and plenty of others. While that's probably not the reason why so many are using 10, I for one would be on 8.1 still.
I was sceptical when I heard that they would actually do that but I was watching a movie and a popup with the update appears, I thought it's for the regular update which asks you to restart or postpone but doesn't proceed without any input, so I ignore it and put the movie back on foreground and minutes later it reboots and starts installing. Thanks Microsoft