Generations aren’t a monolith. It’s reductive to say “these people are leaving because they’re from a different generation.”
The best thing you can do is perform an exit interview and ask them why they decided to move on. If they’re good people they’ll give you an honest answer.
And remember, young people in the workforce now have had adults in their lives who were likely laid off during the 2008 financial crisis. Those adults were, correctly, teaching their children that companies are not loyal to their employees, so do not be loyal to your company.
They are probably leaving for more pay, better benefits, or a promotion of some kind. The only way you’ll know for certain is if you ask.