If you look deeply into it, you'd realize that DOS is pretty awful.
Reliability. It seemed good on that front, but only because it ran one app at a time. If you tried to run DOS Shell and multitask with it, it was horrible.
Memory Management. It's real mode, it works with 640k of program memory and needed multiple kludges to work any better (UMA, HMA). Only way around it was a software protected mode driver (which was only so good).
Drivers. If you install MS-DOS 6.2 (1993), by default these things won't work:
mouse
CD-ROM
sound
video (beyond hardware VESA)
So, you were stuck doing nothing on there until you found drivers and loaded them all. There were none included.
Command line. The DOS prompt was pretty weak, and with no work done on it in ages, it can't do much of anything.
Linux, QNX, and others can scale down pretty well to 4MB RAM, since it'd be stripped down a lot on an embedded system. DOS doesn't have much of a purpose anymore.
[ August 19, 2004: Message edited by: WMD ]