The point is that it's a negative thing to talk about, and frankly sometimes you can't just turn it into a positive story of what you value and how you deal with conflict.
Sometimes a person sees bad shit and just runs, and that's a valid approach. Psychoanalyzing every decision they make is the trap of interviewing.
Agreed, and to move up one level of meta, the interviewer should be thinking about this kind of analysis when they construct their interview process/system.
“How can I moderate this conversation so the questions themselves are not obstructing the candidate’s answers?”
And yes, as the hiring manager, I may want to understand the cultural issues at your last company. Why?
Because I want to understand (a) what you value, (b) how you deal with conflict, (c) will you be able to help me improve our culture here and (d) what cultural issues you may or may not bring with you.
If I'm going to help you be successful here, I do want to understand your background. I may not need all that information before hiring, but I will get to it eventually because it's pertinent to helping you and the team succeed.