Except part of an OS is security. Just like you wouldn't keep an old skeleton key on the front door of your business because of the risk of someone breaking in, you may feel it isn't worth the risk to use an old OS that has an obsolete security model.
The flip side of this is that there has to be an acceptable newer replacement with a better security model. For a lot of Windows 7 users, Microsoft have yet to offer that. (I imagine this is going to cause quite a stir if Microsoft try to stick to their published EOL date for Windows 7 next year, given that still nearly half of Windows users are using it.)
They could create a premium, telemetry-free version of LTSB/LTSC for the several hundred million Windows 7 users who are waiting for the market to provide an upgrade path which supports modern hardware.
If they made Windows 10 Pro more like the Pro edition of earlier versions, i.e., targeted at smaller businesses or power users who want a professional OS but not all the enterprise hassle, I would think they could do very well. But a professional OS doesn't do things like taking control of your computer to update or reboot whenever it feels like it or forcing you to upload any data you don't want to.
I have a suspicion that at some point Microsoft are going to back down on the big deal-breakers. They don't try to push their luck with those kinds of games in their enterprise products, because the big customers simply won't accept them. The frequent failures are just proving the critics right, and there have already been tentative moves to moderate the problems with mandatory updates. If changes in that sort of direction go far enough, they will appeal to smaller but serious customers who aren't running enterprise editions but have similar concerns.
If Microsoft really don't take the hint and back down when it comes to the crunch, I suspect Windows 7 will make the immortality of XP look like an amateurish trial run. I know my businesses all stocked up on Windows 7 machines a couple of years back while we still could, and since then we've been actively investigating multiple possible alternatives to Windows desktops for future use. Looking for alternatives seems to be the general trend across the other small tech businesses within my network as well, so if Microsoft think they're going to call everyone's bluff and get the whole world to migrate to 10 next year by shutting off updates for 7, I suspect they have seriously misjudged their market.
The security as new functionality is not really an issue to keep PCs running relatively safe. The argument that ECC is a new functionality and not a security patch comes to mind. That was a fair argument and people still had RSA. The underlying security breaking is not really an issue today as far as I see it.
The actual deal breaker are bugs who can be exploited and need to be fixed. And while its unfair to expect bug free software, fixing them is not new functionality.
