So basically, Google has too many people for them to be able to list them all. Or Google didn't want to try and list them, thinking they might miss someone, or subject them to poaching.

That seems to be a fundamental problem with humans.txt: The bigger, more interesting a project gets, it creates several reasons why it will only vaguely be able to lost anything, out of a conflict of interest, rather than give full credit to the team behind the site.