We may need at least another data point, but it does look to me that Microsoft has gotten much more aggressive about dropping support for older hardware. It probably a result of Nadella's cut of the Q&A team. If the Q&A team is cut, it makes sense that less hardware would be support, and that you'll also see more bugs in the operating system.
> Despite being Microsoft’s newest and ‘most secure’ operating system, Windows 10 was found to have the highest proportion of vulnerabilities of any OS (395), 46% more than Windows 8 and Windows 8.1 (265 each).
It sounds to me like all of those anti-exploit mitigations that are supposed to come to Windows 10 will be needed just to make it as "secure" as previous versions.
Dropping support? No, said support was announced to not exist before the release of said CPUs, and given that CPUs are a fair bit more complex than appears (for instance Windows XP wouldn't run on Ryzen CPUs until a microcode update in practice due to some old feature being unsupported, or new features would be introduced that old OS task switching code is unaware of) at first glance, it was considered unviable to formally support these CPUs - even if they might work at first appearances, Microsoft gathers sufficient usage/error data that they presumably know of some hard-to-fix issue that makes it impossible to guarantee the OS to work together with this new hardware.
Also, an update to the OS to make it compatible could potentially be sufficiently high-impact that it could break user applications, existing hardware functionality, or other potential concerns.
