Frankly, I think that in most cases, exit interviews are a self-delusional process.
When management creates an exit interview process, they are thinking, "We will find out why employees are quitting. When someone is leaving, he presumably has no reason to fear any sort of retribution -- obviously he can't be fired or given undesirable assignments or whatever, as he's already quit -- so he has no reason to not be honest. So we can learn what is really happening there in the trenches, and we can fix problems."
But upper management is human just like all the rest of us, and tend to justify themselves. So what REALLY happens very often is that whatever complaints about the company these departing employees express, management concludes that the employee just doesn't understand the totally valid reasons behind company policy, and so dismisses the complaint. Like, an employee says he quit because the people who get promotions are not the best qualified but those most adept at office politics. And so the boss says, "Oh, he just has sour grapes because he didn't get the promotion he wanted, I'm sure the person his boss did promote really was the best qualified."
It reminds me: I used to work for a company where every year we had to fill out a self-evaluation form that was supposedly part of determining our annual raise. One of the questions asked if there was any company policy or procedure that we thought should be changed. (Not the same as an exit interview but in the same direction.) The first couple of years I left this blank. My third year there I wrote that procedures for arranging business travel were unnecessarily complex and I suggested a couple of simplifications. My boss wrote that he had explained to me why current policies were necessary. He hadn't explained anything to me, but I got the message that nothing was going to change. A year or two later I suggested some other policy change, I forget what now, and -- I had a different boss then -- my boss returned the form to me and told me that I should prepare a new form leaving this blank because upper management didn't like to be told that company policies were misguided. When that boss left the company I was assigned to clean out his files, and I came across a memo he had written about another employee (I probably should not have seen memos related to personnel matters, but whatever), that this employee had complained that he thought some people were given preferential treatment, and so the boss and the boss's boss "counseled" him on how the company was completely fair. Apparently after a few hours of browbeating ... I mean counseling ... he said "I probably shouldn't have written that", which management took to mean that he now realized how wrong he was.
And I thought, Why does the company ask the question, if the only acceptable answer is "no, I have no suggestions because company policies are the most perfect that anyone could possibly imagine", and any other answer gets you into trouble? Once they've browbeaten all employees into keeping any suggestions to themselves, do they then congratulate themselves on how happy all the employees are?
And that was a good company to work for, I was basically happy there and stayed for 12 years.
Upper management THINKS that they want to get feedback from the people in the trenches. It makes sense to want to know whether morale is high or low, and why. But in reality, for most managers, if somebody below them tells them that they're making a mistake, their immediate response is to get defensive and explain why what they're doing is, in fact, a good idea. If you don't agree it's a good idea, the problem is that you don't understand.
Hey, we're all like this. It's very difficult for people to admit mistakes. Doubly so when they come from people "below" you.
Oh, I'm sure there are some companies that take employee suggestions and exit interviews seriously, and that really take action based on employee's comments and complaints. But wow, I'm hard pressed to think of one that I've worked for. :-)