There was a fair amount of software written for DOS that never made the jump to Windows (or any other OS) and some combination of hasn't been economically viabl

There was a fair amount of software written for DOS that never made the jump to Windows (or any other OS) and some combination of hasn't been economically viable to redevelop and/or people just really liked the way the DOS app worked. One common use case was control/monitoring software for some specialized piece of external hardware such as test/measurement equipment, security, HVAC etc. Much of this has modern substitutes available on current platforms, but it requires replacing the hardware as well as the software. Given that people paid 5+ figures for this stuff back in the day and if it still works, might as well keep using it until the wheels come off.