It's the jump from Windows 8.1 to 10 imo. That was when their strategy shifted from Windows being a sold as a product in-itself towards being used as a vessel to push people towards other, more profitable Microsoft services.

In the modern age of PCs, it's just not profitable to sell an operating system as an end product anymore because consumers expect the OS to be available free of charge, like it is on Apple products and Android devices, so the only people actually paying for Windows are OEMs who pay like $5/key, which isn't enough to sustain a profitable OS without bundling a bunch of third party shitware, steering you towards paid Microsoft services like OneDrive/Office 365, and selling all your data