It peaked at 4.05% in March. The last 2 months it went just below 4% as the Unknown category increased. For June the reverse happened, so 4.04% seems to be the real current share of Linux on Desktop as desktop clients were read properly/werent spoofed.
There are system dialogs that have unused space for ads, still plenty to improve!
In all seriousness, cloud (azure) and office subscriptions blew up and account for like 70% of MS profits. They know the Windows experience is lacking, but when they already capture so much of the market and it’s such a small slice of revenue, they have no incentive to improve.