Yeah, because Microsoft's stock was shit when Jim Cramer invented that acronym.
That may be the original etymology, but to this day Microsoft isn't considered a top-tier tech employer compensation-wise. So lots of engineers saying "FANG" or "Top N" or whatever aren't including Microsoft in it for that reason. So there's basically two different but related definitions going on here, but we're specifically talking about their desirability as an employer, not "the biggest tech stocks".
OTOH, I have heard a lot of people that have done both MS and FAANG say MS has a superior WLB in -most- units.
And they pay less as a result. It's always been out there that MSFT, Apple & Amazon pay less than F, N & G unless your a special case. But you get paid more if your special case everywhere anyway.
On the other hand there is an M in "MANGO" (the O stands for "Opensource").