One of the pieces of advice that is drilled into anyone that is looking to improve their interview skills is to _never_ criticize previous employers. This question practically begs for that. As a result, a hiring manager is practically guaranteed to get awkward stilted answers from candidates who are trying desperately to frame their response in a way that doesn't criticize the previous employer.

It is all a head-game, sadly.

Candidates never really know if their dealing with someone who expects smooth, calculated responses or if they're dealing with someone who expects brutal uncomfortable truth.