I would easily blame Windows 10. Automated forced updates, in file-manager advertising (although to be fair it's just for their cloud file hosting offering so it doesn't bother me half as much as it bothers most). There's other things as well, and Windows 8 the previous incarnation was not well received either. Microsoft really needs to revamp their entire OS team because everywhere else in MS land people are getting happier, but when it comes to the OS itself people are still upset. I've been using Ubuntu / Linux for as long as Windows 10 has been out. I used to use it on and off, but now that Linux is usable on some of my more modern hardware it's hard to switch back. I only use Windows at work for .NET development.

Why would some backlash against Windows present itself all of a sudden in a 1-2 month span now?

You're also using a lot of "I". Windows 10 has been received decently by the public. Windows 8 wasn't but it wasn't the worst reception either since a lot of people were so happy with Windows 7. This could possibly make sense if Windows 10 hadn't come out. But even then the number increase is too great in a short time span to blame Windows 8/10