I did. Linux and OSX are still available for whoever wants them. You can stick with Windows 7 if you want, that's just fine. I like Cortana. I like my software knowing what I like and what I'm interested in. It makes my life easier, which is what computers were invented for.
I can see why some people might not, and to be fair I use Linux on my work laptop because the work I do demands it. I would never put my client data on a Windows machine.
But like I can see your side of the argument, you have to be able to see that some other people want personalization and learning and all that. Pandora and Apple Music are both heavily tailored that way. Google Now on your phone knows everything you do. Netflix can find videos for you to watch based on what you've watched before. Amazon will recommend purchases to you based on what you like. Hell, half the people on this site build these systems. You know how many machine learning articles there are on the front page every week?
So who wanted that? I did. And so did several million other people. For the people who don't want it, I mean it's not even really opt-out. They ask you up front do you want the default or do you want to pick your own privacy settings. If you still don't trust it, Windows 7, OSX, and Linux are right there, just a click away.