People have different preferences for what they like to work on, but you seem to be implying the weather app engineers are incapable of doing that work. Like they're some kind of lower caste that must be kept away from working on security mitigations for filesystem drivers.
I don't believe there's some category of human that's capable of shipping Windows 10 feature apps, and only that. People can move internally! People can leave and other people can be hired. It's all priorities and task allocation.
The impression I get (and please correct me) is not really that there's an oversupply of news feed app builders on the market, but that the Windows team at Microsoft has been shifting to more user-facing features rather than internal deep kernel work.
I'm pretty sure that a developer that wants to switch can and not many kernel developers would be impacted in total.
Besides, paint and notepad getting a make-over doesn't make a dent of difference for a company at this size.
Also that weather-widget engineer could do some basic tasks offloading more experienced engineer, who would offload even more experienced engineer until that chain of offloading makes enough time for NTFS-ninja to hunt down and fix that bug or write a fuzzer that finds new zero-days.
If you use MS, then it's Microsoft s fault, you won't be blamed because almost everyone was exposed to it and you got hit.
These companies also have older workforce who are used to windows and the switch would be difficult. Yes I know some older users would be fine but that is not the majority.
It's similar to the "no one got fired for buying oracle" situation
Being Linux-based does not preclude support.
I don’t think it’d be possible to train the React dev in kernel programming unless they had a serious interest in low level stuff to start with.