You could run the 286 in Protected Mode, which offered those features. The problem was that DOS programs needed to run in backwards-compatible Real Mode, and sw

You could run the 286 in Protected Mode, which offered those features. The problem was that DOS programs needed to run in backwards-compatible Real Mode, and switching between them meant resetting the CPU. You could implement a competent OS for the 286 (Coherent, Minix, Xenix, OS/2 1.x), but it wouldn't be able to run DOS programs - though OS/2 1.x managed to swap between one DOS session and all of its OS/2 sessions. With the 386, you could run multiple virtualized Real Mode CPUs, which enabled OS/2 2.x to preemptively multitask DOS sessions. Windows 3.x on a 386 or higher could also multitask DOS sessions, just much less reliably.