It already is an ad platform. They want to turn it into the surveillance platform of choice for governments, businesses and law enforcement alike.
Windows is already a privacy farce. The OS and 3rd party drivers capture a large chunk of what you do. Imagine having everything you do in one tidy location that can and will be used against you at the drop of a hat.
Even tough I like to be on Microsoft ecosystem, I have to acknowledge that Azure is the new golden goose in terms of Azure OSes, now that we are back into timesharing.