We aren't the customers. The advertisers who pay to show up as Search Results are the customers. That's why.
We are the customers though, that's why it's so tragic a fall. I spent something like $200 for Windows. Microsoft doesn't get to use that excuse here. It's not some free service like Gmail; Windows is paid. See also the OneDrive advertisement fiasco.
I think Windows started going downhill for two reasons: When Microsoft coopted the desktop version to add mobile-oriented features (Windows 8), and then when they coopted it to start cross-selling their cloud and Web services.
You have to wonder: how is it that a single developer can build something so much better than a behemoth like MS? They should be seriously embarrassed.