What is MS's end game here? The development cost savings seem not worth it. The only plausible reason I can think of is collision with PC manufacturers to boost sales.
1) For the past two decades, "botnet/vector as a service" has been a hidden feature of every unpatched internet-connected Windows system, and Microsoft since Windows 10 have been enforcing policies that signal their stance that platform security isn't elective. Dropping or locking support for Windows on vulnerable hardware is a logical next step if the next guess is true.
2) Like Google and Apple, Microsoft has fully entered the Global Identity Services game, and forcing TPM is necessary for their vision of a complete digital identity, from endpoint to cloud.
They've been blurring the lines between desktop and cloud for years, and the Microsoft Account is going to be their passport to accessing your games, apps, and files on your home PC anywhere. I mean, it already is, but it hasn't reached peak mindshare in enterprise where they're competing with IBM and other identity and access management providers.