I don't know of any recent comments on behalf of Microsoft regarding encouragement for using third party antiviruses, but if you're referring to the news articles from the 2013 well then it was a
misinterpretation by media and was
promptly dismissed by Microsoft.
If there is any new announcement regarding this from Microsoft, then please help me to find it because my Google-fu is failing.
Well Microsoft handles PR pretty badly, and to most average joe norton and McAfee are the only AV vendors, everyone else is trash. That's just lack of knowledge nothing else.
I am not saying every antivirus trashes PCs regularly. But it's not uncommon, almost every year we get a case. Third party AVs are all susceptible to this because they don't know windows as good as MS, so they have more chances to trash it. And when this happens, it hurts pretty badly because in many cases a fornat and restore is only way.
Also windows defender is also the AV that has least conflicts with other softwares. In my personal experience I turning on ssl scanning in ESET nod 32 broke Firefox for me, so things like this keep happening all the time. Third party AVs have good detection ratio but they come with their own caveat.
After witnessing the windows 10 upgrade fiasco, I strongly agree with you in this one.