I don't think recruiters and hiring managers realize how bad the advice to "be truthful about why you left your job" and "don't bash your manager" is to candidates when put together. If you are asking "Why did you leave your last job" and expecting both honesty and not hearing about how bad management was, you're just setting candidates up for failure and accepting that the people you hire are those who know how the game is played and are willing to "tell a half-truth" about their reasons.
Look, sometimes you have a terrible manager. Sometimes your manager has an even worse manager. Sometimes you're being harassed. Often the environment is racist or sexist or both and nobody is being held accountable to fix it. We speak a lot about diversity and creating great teams, and then we refuse to hold companies accountable. It's a mess.
Either we accept that the question is built for those who know how to game the system and the consequences that come with this, or we stop asking and find better things to ask that get you the same information.
I've been guilty of asking before, too; the reason it's bad is that it's designed for the candidate to fail.
A better question is "What are you hoping to get out of this role?" or "What are some skills you want to get in the next 5 years?" which puts the candidate at the center of it and the company and manager as tools to get them what they want.