Feels like we remember MS-DOS as simple because it fit the time. One user, limited hardware, not much going on in the background. As soon as you try to add multitasking, networking, or even basic isolation, that simplicity doesn’t really hold up.
That does not mean that we need things to be as complex as they now are though.
I mean, when it came out, people didn't really need much of that
Well… it was still far more simple than anything today. Whether we are looking at Concurrent CP/M-86 or at Multitasking MS-DOS 4, these were far more simple than anything OS today. Once we add many users, you start looking at things like Xenix and other early Unices. Those too, we’re more simple than anything today.