Perhaps you got hung up on that whole "Generations"-Thing. Generations cannot be defined by common attributes as easily as it might seem. Perhaps the explanation is less the "generation" but more the age of the people? Younger people are more likely to quit a job because they have less responsibilities that would keep them from doing so if they start to dislike their current job. Gen X/Millenials are now all in prime family-establishing age and thus more likely to prioritize job security over job excitement. Younger people might weigh this differently and switch around to try other companies/other fields.

Were they being paid at a similar level to their generally older, more experienced co-workers?

While there certainly could be a wide variety of possibilities, age as a factor has a correlation with so many different things, it's wise to narrow it down a little bit by eliminating the most obvious possibilities. Financial compensation is an extremely easy first one to consider, as a factor.

I can tell you why I'm quitting. I'm a millennial. I generally loved the people I work with. I like the work environment. Or I did. We have several old timers quitting right now. The attrition rate is through the roof. Retirement is upon a lot of the old guys and they're leaving either for better jobs or for ones that are less stressful if they aren't retiring. The younger ones (millennials and gen z) don't see the point in sticking around if the older cohort leaves and take their knowledge with them. There's no one to train us, and worse still, changes to the way that my worksite is managed make staying untenable. We don't want to be left holding the bag so to speak. Blamed for low productivity after the older guys are all gone and the knowledge gap becomes more apparent. We aren't really paid well enough, and we don't see the kind of COLA adjustments we should.

Additionally, there is a shortage of us, we have expenses on tools and so on that add up and the company I work for doesn't manage slow times and busy times. So I can't even count on overtime. Sometimes it's mandatory. Sometimes it's nowhere to be found.

I have brought up multiple issues with safety and legal responsibility and been told by my manager that they need to think about it - repeatedly. I feel like my concerns aren't being addressed. I want a good home/work balance. I spend 10 hours or more a day at work, and sometimes that's 4 days a week sometimes it's 7.

Worrying and stress are a big part of why I am leaving. I don't want to be worried or stressed all the time. I don't want to think about work outside of work.

You sound like a good boss who is engaged in the development of your employees. That's good. But sometimes it's just that we often take jobs because we have to, not because we want to. And when something better comes along we feel like we have to take the chance.

What did they tell you when you asked them?

Treat them as normal understand them listen to them you should be good

My company has struggled with this too. We’ve lost all the Zs we’ve hired within the first few months, and we were deliberately trying to mentor them so they could gain the professional skills they were very clearly lacking on hiring. I invested so much of my time training them on how to write an email, how to write a document using complete sentences, how to proofread a document, and how to be in a meeting (4 different Zers individually, who could not do any of these things without significant hand-holding).

Once we were happy that they were up to speed and on the same level as the rest of the team, they left. Consistently their reason was “thank you for giving me the skills I needed to get a better job.” Which, great! I guess. But that leaves me pretty stumped. How am I supposed to train new team members knowing that they’ll leave at the first opportunity? I’m not a manager, so it’s not really my problem, but ya, it’s frustrating for this elder millennial who just appreciates having a job that isn’t exploitative.

I think, like others have said, an exit interview is your best bet if you really want to know.

We don't know anything about what it's like to work for you, what you do, what everyone gets paid, etc. Tell them you want to know and they will most likely be happy to tell you.

Are responsibilities being spread fairly or are older employees dumping the shitty work onto younger employees? Does the workplace unfairly reward employees based on how long they've worked there? I've worked in those environments and it sucks.