I haven't worked in your this industry, but I've built, trained, and retained teams in highly-competitive industries when turnover was high due to skyrocketing compensation offered by competitors.
The general advice I'd share is to take inspiration and operational hints from organizations who have dealt with this problem for a long time-- like software companies. And like most things in life, it's really about the people and the systems you have in place to motivate and support them.

More specifically:
- Read the book The Dream Manager by Matthew Kelly
I've not read it in years, but it's stuck with me for over a decade. He walk through advice on things like creating a dream manager program at your company and how and why this is so impactful for people who might never have experienced an engaged and communicative manager before. There's also specific guidance on how to approach people as individuals who have different personal goals than perhaps you have. Just lots of good stuff.

- Build a culture of trust
This sounds cliche, but the fact is that some of the best employees intentionally de-risk their career by working with people whom they both trust and admire. If you can give them trust and stability, you'll find that they are far, far more likely to stick around.


- Make your business attractive to the kind of people that stick around
Building a business is risky and some folks just aren't excited by that. Create an environment that rewards loyalty and stability over risk-taking and many folks of this type will naturally self-select. When you find those people, work your butt off to retain them.

I've been a bit wordy so I'll end it here, but I'm happy to add any details or answer any questions if there's an indication that folks would find it helpful.

This is an challenge across all sectors. The lower the barrier to entry, the increased likelihood of trained management leaving to start their own business. The key in my opinion is to incentivize the person to stay by offering them equity in your business. The upside needs to be there for them to stay and so if you help them get what they want, they will stay. It may be 10% equity vested over 5 years or it may be 25%. The point is to figure that out and make them a partner. Good luck.