You're right. Windows for Workgroups 3.11 isn't getting patches for Kaby Lake either. Those evil bastards.
https://www.netmarketshare.com/operating-system-market-share...
Windows 7 still has twice as large install base as Windows 10. It's literally nothing other than MS stopping support for 7 because 10 is out - imagine the outrage if Tesla stopped supporting an older model S because a new one was out.
IIRC, the compatibility problems with the new processors are processor drivers and power management.
However, the dumb thing is that Microsoft already made the engineering effort to support those things, since they used to support Windows 7 on the now-unsupported architectures. Now they're taking it away to push Windows 10 some more.