Comment by kprotty

Preemption simulates localized concurrency (running multiple distinct things logically at the same time) not parallelism (running them physically at the same time). You can have concurrency outside continuations. OS threads for example are not continuations, but still express concurrency to the kernel so that it can (not guaranteed) express concurrency to the physical CPU cores which hopefully execute the concurrent code in parallel (not guaranteed again, due to hyperthreading).