Because of the spyware, because of the in-system ads, because of the two control panels, because of the frequent and uncontrollable forced reboots, because of all the embedded nagware (try skype, try office, try onedrive, try cortana, try candycrunch, try bing - it will make your premium laptop feel like a cheap device purchased at Walmart). Let's be honest, it's a junk OS. And because if you upgrade you loose control of what features you will get (microsoft will force you to accept updates and upgrades), and God knows what other moronic decisions the guys who brought you windows 8's "all apps full screen", the contextual menu at the other side of the screen (bright idea on a 4k monitor!), etc, will force on you with no way to opt out.

And the cavalier approach that Microsoft is adopting to force that upgrade on their users is obliterating the little faith and goodwill I had.