I would also imagine that, especially during interviews, they recognize their duty is in part to sell the candidate on the firm. There's an implicit pressure to be positive about your company because there's only downside to saying negative things, even if it's honest. I don't see why an employee would put themselves on the line with a candidate, who they may never work with nor see again, just to express what they think is right.
If you're trying to hire "top 10% pay at FB" smart level people, hiding behind poorly constructed rhetorical barriers is more of a negative thing than recognizing a real negative thing. It doesn't have to be anyone's "fault" even, but more of a consequence of the system that was built with good intentions.