Sadly, I don't have a reference handy, but I recall reading a while back that there was this toxic culture at Microsoft in the past where one of the easiest or least frictive ways to climb the ladder professionally was to undermine others due to the way performance was evaluated. Basically, something of a “cull the lowest performing members” model.

Not sure if this is related or even reality, my memory wasn't so great even when I was young.

That was the model Ballmer implemented. When Satyer Nadeller took over they removed this insane and destructive system.

Windows and MSDOS teams were very close, no issue there.

The real reason someone might need to do this hack is that there were in fact many versions of "DOS" not made by Microsoft. These included Zenith, Compaq, Digital Research and IBM. Each of these each had their own subversions.

IBM DOS was basically MS-DOS (except IBM did do some of their own work of course). Pretty sure Zenith and Compaq DOSes were OEM MS-DOS (Zenith did have a "Z-DOS" but it was just another OEM version of MS-DOS for a non-IBM-compatible system). DR-DOS was of course a true third party DOS (one of the very few contemporary ones IIRC)

Reading the source code (which is available on archive.org) you can see exactly this. Lots of IFDEF statements for compiling MSDOS and PCDOS differences. When I first saw that, I was really surprised.