Until very recently, Microsoft's business model had not been about profiting off collecting user information. They were one of the last remaining companies who didn't attempt to monetise the crap out of their users.

For the same reason people freaked out about a very easily disabled Amazon search integration in Ubuntu. People had higher expectations of Microsoft (and Canonical) than Google. Plus, the desktop / laptop environment is one in which regular monitoring outside of the browser is something usually only done by malware.

Microsoft should have recognized they were considered more trustworthy, in one sector anyways, than Google or Facebook. Building on that trust by building a Windows 10 with great privacy would have helped their reputation and stemmed the bleeding a bit. At any rate, I have no idea why MS doesn't just allow a "disable all tracking and telemetry" option on all versions of the OS. Would kill most of the complaints immediately, and most people wouldn't bother opting out so Microsoft would still have the data they think they need.