Just because of the enormous and mostly upfront cost of doing it. “My department needs 100 new PCs that will run Win10.”
Anyone who’s been through this kind of exercise in any large organisation knows that it (a) takes ages, (b) uncovers unexpected problems that need solutions (“my printer doesn’t work any more”, “the software we produce gives different results now”, “the people still on XP can’t talk to the ones who have migrated to W7”), and © [that is NOT what I meant, Medium!] offers only marginal productivity improvements as people find new ways to waste their time.
We little people are encouraged to upgrade so that we get used to using the new things and solving our own versions of (a) (b) and © in our own time, and manufacturers can then say to the big orgs “If you want support for these old things that nobody else uses, it won’t be free any longer. Your choice.”
There are plenty of other ways to be spied on. Not having them built-in won’t prevent it.