I would assume because it's hideously expensive to maintain a full OS and support and compatibility guarantees with all the random horseshit consumer platforms throw at them, and they did the math and concluded they liked the profit margins for purely online and non-consumer targeted things, where they can more effectively constrain what is and isn't supported, better.

In particular, my guess is that they looked at their estimates for how much they could make off recurring revenue sources in desktop OSes, and their estimates for how the desktop market is changing with more younger users not using them or viewing them as legacy platforms, and decided they should pivot to primarily being a services provider, in much the same way they're aggressively trying to slap the Xbox branding on other things and getting out of the console market as fast as they can run.

Could be wrong, I don't work there, but usually my experience with companies that large making apparent missteps is that their goal isn't the one you think it is, and attempting to extract as much data as they can from desktop users really sounds like what you do when you're trying to squeeze the sponge before you throw it out.