At that time, they were not offering salaries that were even competitive with other companies in Madison. Never mind about Seattle or SV. I had four managers in 2.25 years, because three of them left for higher pay elsewhere almost as soon as they got promoted. I left the fourth for ~20% higher pay.
I would guess that any major tech employer could stroll into town and hire the best 50% from under Epic's feet in less than two weeks, while still saving money on salaries compared to SV. Queen Judy is not taking that company public, and would rather divert her profits to charity than to employees. There won't be options or RSUs. The only reason people might stick around is the cult-like atmosphere.