To fill in one gap - our hiring process has an extra layer of insulation to better control individual biases. Your interviewers all submit feedback and an independent hiring committee makes the decision, on a different day, with all due deliberation.
The reason nobody has anything to say to you at the end of the day is because none of that has happened so nobody knows what to say at that point, and I don't think it's likely to make you feel better to have somebody give you a completely generic speech that has got nothing to do with you.
As for the more general thing that keeps popping up - do people seriously believe that all the thousands of Google engineers who do interviews haven't figured out that people writing code on a whiteboard under stress aren't the same thing as people sat at their desk grinding out code?
Of course they know that writing code on a whiteboard under stress isn't the same thing as sitting at a desk grinding out code. The problem is that it's pretty hard to sit down all the applicants for a position for a few weeks and work with them long enough to actually get a sense of how they work, and it's quite wasteful for the 95% who don't get the job.
Some companies actually do this, eg. Coinbase requires that you take a week off from work and work with them (I think unpaid, but perhaps you get contractor wages) on a project. They've been widely criticized as exploitative here, with many people saying "Why should anyone who has any choice at all agree to that?" They also open up a rats nest of legal & IP issues.
The best way to get a full-time position at Google - or most companies, really - is to get an intern or contractor position and then convert to FTE at the end. Hiring rates are way higher for successful interns (and the interview process is shorter), because they have lots of people inside with first-hand experience grinding out code with them that goes directly into Google's systems. But getting that internship or contract itself often requires an interview...
Yes, "thousands of Google engineers who do interviews haven't figured out that people writing code on a whiteboard under stress aren't the same thing as people sat at their desk grinding out code?"
I am pretty confident they don't know that. I know people way smarter than me who flunked the google interviews and, working in the same building, know even more that got in who are very good but not great. Also, they are ageist and "don't consider experience at all" (and that is from a direct quote from a person in an interview).
The reason nobody has anything to say to you at the end of the day is because none of that has happened so nobody knows what to say at that point, and I don't think it's likely to make you feel better to have somebody give you a completely generic speech that has got nothing to do with you.
As for the more general thing that keeps popping up - do people seriously believe that all the thousands of Google engineers who do interviews haven't figured out that people writing code on a whiteboard under stress aren't the same thing as people sat at their desk grinding out code?