That is an excellent question and one worth answering in detail. Windows 11 is a failure because:

• It failed to meet a reasonable level of quality. It simply wasn’t tested enough. There are still a lot of bugs and glitches being discovered, 6 months and several updates after release, while it’s obvious to everyone that many aspects of it are still incomplete. In fact, some are still under development right in front of our eyes with every new Insider build. That is unacceptable.
• It failed to fulfill Microsoft’s own promises regarding new features and functionality that was announced but not delivered. Building up hype about things but having no intention to have them ready for consumers at “launch” is also unacceptable. It would be better to announce features actually ready to ship and then add new stuff gradually and steadily — but, then, the launch of Windows 11 would have seemed even more underwhelming, see?
• It failed to be actually better than its predecessor, which is the whole point of developing a new operating system. It’s not lighter on resources (not really), it’s not faster or more performant at anything, it does not help most consumers do things more easily than before (sometimes the exact opposite). That is, in and of itself, a reason to call it a failure altogether.
• It failed to properly — and satisfyingly for us journalists — explain how and why its security is strengthened by Microsoft’s choices regarding those hardware requirements. Sure, one can understand how TPM is a useful feature in general, but the almost arbitrary way of setting that CPU hard line is still upsetting to many. Security was supposed to be the one thing Windows 11 had going for it and Microsoft managed to mishandle even that part.
• It failed to even do what Microsoft and its partners were obviously hoping, that is “scare” or “bully” people into getting a new PC for Windows 11. Data for Q4 2021/Q1 2022 suggest that there was no sales boost to speak of, the traditional effect a new Windows version usually has on the PC market. Sales were in line with what’s usually happening during these quarters. Nobody went out to buy a new PC because it comes with Windows 11. People bought the PCs they would probably buy anyway, those just happened to come with Windows 11. That’s all.

Most of all, though, Windows 11 failed to create excitement in the Windows community, which obviously has something to do with all of the above. People just did not see the point in upgrading. When one is offered a new version of the world’s most popular operating system for free and he/she chooses to pass, in my mind that is the very definition of failure on Microsoft’s part. People just dismissed Windows 11. Simple as that.

In the coming years, Windows 11 will increase its market share, sure. It will do so through the sales of new PCs. I also fully expect a decent percentage of current users of Windows 10 PCs that are upgradeable to make the transition at some point in the future, when they feel that Win11 is safe to use and much closer to what would be its “complete” form.

But of the set of objectives a new operating system strives to achieve when coming to market, Windows 11 achieved none. Is its failure even up for discussion? When are we supposed to make the call regarding its “success”? At some point in 2027? I do not see it that way. When people make the conscious decision not to use a product that’s offered to them at no cost, that is all I need to know.