Honestly Im not really sure how profitable that would be for them. Most people dont really think about their computer OS much, they use windows because thats what they know how to use, because their computer came with it and they've not tried anything else. Businesses might think more about what they use, but their employees know windows and training them on other things would take time and money, so they too use windows. But if windows becomes a recurring subscription instead of something you buy bundled with the computer itself, then that would force people to think more about it, and potentially seek alternatives, like Linux or whatever else might come up. More use of those alternatives would lead to more software being made that supports them in order to not lose those sales, which in turn makes non-windows OS's viable to more people, which would cause more people to actually switch to them, and so on. This could eventually lead to business customers eventually deciding it would be viable to try something else, which could ultimately lose Microsoft money. Being the "default" OS gives them an effective near-monopoly on that market, they would be pretty foolish to risk that I would think, especially when as you already mentioned, other ways of monetizing those home pc users like ads, or for that matter selling data to advertisers, already exist.