Microsoft used to have a group, Trustworthy Computing (TWC), that was where all the security expertise lived. TWC was destroyed in 2014. From the outside, it seemed like that was the point where the reporter/outside security engagement story stopped, because the people that held responsibility for it Microsoft wide were either fired or re-orged into a role where they didn't have broad authority any more. Now, you get stuff like this, where people on the "security" group (which is squirreled away in a totally different part of Microsoft) don't have visibility into the Edge bug tracker any more.
Internally, Microsoft is organized a lot like the Federal government, only worse.
One can see a rationale in not having a security group - every team should have security focus (eg by having expertise & champions within each group). You can't tack on security, you have to build it in.
I disagree - the motivations of the security group and the product group are different. If the security team is under the product team leadership, the security team is disincentivized to interrupt a product launch due to a security issue, because they're rewarded by shipping a product, not making it secure. Really, you should have both: you should have a security team that sits with the product team and works with them through the lifecycle of the product, and has continuity (i.e. it's the same security people with your product team through the life of the product, mostly), but that security team reports to different management and has their promotions, bonuses, etc. handled by a different leadership chain than the product team.
Internally, Microsoft is organized a lot like the Federal government, only worse.