Or, more likely, so they can fucking monetize your usage like the greedy self entitled assholes they are.
And I don't just mean Microsoft.
It depends upon the corporation. With Windows they're going to track your usage data to improve the product. Microsoft would be over whelmed by uploading every computers key strokes every day. So each machine is configured to only upload on certain days. Plus every time it's uploaded, the user id, is given a different GUID. Microsoft couldn't track Windows usage data back to a single user if they wanted to. Let alone wrap it up into an advertisable unique user product. They can do this because there's a large enough user base that they a small slice still represents enough people to get how the product is used.