That's something I can't answer, but I think you can thank the group of
trolls who regularly spammed the MS groups for the decision. There are a
multitude of web based forums that also harvested the groups, maybe that is
also part of the reason.
The Answers forums are official and are moderated. As well as the well
known, and appreciated MVP's, there are MS technical people offering
assistance.
I understand MS will eventually close all the groups and shut down the
servers they have contributed over the years. Many ISP's have discontinued
offering newsgroups already, and that trend will continue. These days people
expect graphical sites, not vanilla text ones. Newsgroups will go the way of
bulletin boards. Personally, I prefer the newsgroups, but the trolls did
ruin the enjoyment and hasten the demise.