As employees realize they’re getting a bad deal and that they can find a better ratio of pay to hours worked at other companies, they leave.
If I'm an employee with miniscule equity, why would I put in any more time and effort than what was agreed?
If it’s a great company, people will work extra hours to move ahead, knowing it will pay off in their careers. “Great company” is always relative to the individual and where they are in their careers.
As people mature in their careers, they split off into “people with equity who continue to work hard for it” and “people without equity who have a good work/life balance”.
But as long as there’s the promise of a life-changing development, people will (sometimes rationally) work outside of their agreed hours.