The guide is stuck in some false then versus now thinking.
A preemptible kernel isn't "modern". Cooperative multitasking isn't "old".
These are just choices in the design space that can be relevant at any time.
Fully preempted real-time operating systems existed many decades ago.
Meanwhile, today, there seems to be a renewed interest today in coroutines and fibers and such, and they are showing up in programming languages. Those mechanisms are forms of cooperative multitasking.
If you need an embedded system to do a few simple things, why would you threaten its stability with preemptive, interrupt-driven task switching?
A preemptible kernel isn't "modern". Cooperative multitasking isn't "old".
These are just choices in the design space that can be relevant at any time.
Fully preempted real-time operating systems existed many decades ago.
Meanwhile, today, there seems to be a renewed interest today in coroutines and fibers and such, and they are showing up in programming languages. Those mechanisms are forms of cooperative multitasking.
If you need an embedded system to do a few simple things, why would you threaten its stability with preemptive, interrupt-driven task switching?