Why do people leave jobs quietly when dealing with a toxic manager instead of calling them out?

I’ve noticed that many people who resign due to a toxic or narcissistic manager often leave on a polite note, like: “I’m looking for a role that aligns better with my working style/career goals.”

But here’s my question:

Why not call out the manager in your resignation or exit process? Even if you know HR or leadership won’t take action, wouldn’t it at least prepare the company to be more supportive for the next person stepping into your role?

If you’ve been through it, wouldn’t you want to prevent the next person from going through the same ordeal?

I’m genuinely curious:

1.  Are there unseen consequences if you mention the real reason for leaving in your resignation email?
2.  Do you think this approach (calling them out) is even worth it, especially if no action is likely to be taken?
3.  For those who did mention the toxic manager—did it help anyone or just backfire?

I’d love to hear people’s perspectives or experiences. It’s something I struggle to wrap my head around because staying silent feels like enabling the cycle to continue. I should add that this is a very small company so expecting things to improve for the new person. Also, my skills are not limited to a particular industry so I don’t think it can harm my future opportunities.