In this case, they probably didn't want to be too explicit about the details of patching tens of thousands of machines while the remediation was still ongoing.
I do agree that it's unexpectedly hard to find a link to the "security notice" page anywhere.
Also, how'd you find that link? If you happened to just have it laying around, that's fine but it would be better if they had these things linked somewhere customers can find them when new ones are posted (like a page covering service post-mortems) and the timeline is missing little details like the year when the outage happened and a point of contact (it's signed by "the aws team") if you have questions.
That's a great point. I found it by googling "AWS post mortem", but I only knew it existed because I had been linked to this page before.