The recruiter told me I had 3 really positive reviews and 2 somewhat positive and 1 negative review. It's usually more feedback than I expect from companies but it was good to hear. It also matched with my expectations knowing how the interview went. She apparently took it to another hiring committee and they said no as well.
That's true at a lot of organizations. The cost of a false positive hire typically vastly outweighs the cost of a false negative, particularly when you have the luxury of being perceived as a premiere employer in the space (from which follows a steady stream of qualified applicants).
I know the rationale. Then again if it's just one 1 person out of 6 (including 3 other persons who gave "very positive" reviews) then maybe that one person is just being ... negative. As the modern interviewing culture (not so subtly) incentivizes them to be.
In my case, it was the recruiter in Dublin, where I interviewed, writing "it looks like we are coming to a successful conclusion" about a week before I got the generic dismissal email.
(A quick note/disclaimer: I am extremely happy in my current situation, and work for a great manager; no interest in moving, despite my flippant comment.)
The signal was what I was told when I got a subsequent unsolicited contact from a Google recruiter. She communicated this information to me verbally. (I believed her, and in retrospect still do. She was great during the whole process; never gave me the slightest indication that she was in any way deceptive or dishonest.)