I'm guessing this is an informed business decision on their part. It boils down to a pretty simple inequality: Supporting older versions of Windows in the new

I'm guessing this is an informed business decision on their part. It boils down to a pretty simple inequality: Supporting older versions of Windows in the new Office is only worthwhile if the expected additional profits from sales to people who have decided not to upgrade to Windows 10 are greater than the expected additional development cost of supporting older versions of Windows. Probably there's a fudge factor in there, too. Probably, that fudge factor nudges things away from supporting Windows 7, because Windows XP. I'm guessing it also nudges things away from supporting Windows 8, because I don't know of many people who were willing to upgrade to Windows 8 but no further.