Microsoft fired their testers in 2018 [1]. Since then we've seen a surge of pretty serious bugs, some of which had to be pulled [2]. Not saying this is related, as this is a vulnerability and not a bug in an update, but 100 days to release a patch is telling.
>"The number of apps in its Windows Store had dwindled to 13 percent of the 1.1 million offered in 2014, the company said, and it needed less bug testing from Lionbridge, according to a January 2017 memo obtained via a FOIA request."
[1] https://news.ycombinator.com/item?id=17830381
[2] https://www.theverge.com/2018/11/13/18090982/microsoft-windo...