Startup employees make less money on a nice exit, but aren't as committed and can work for a few companies (maybe 2 years each) to improve their odds.
So having 10 years to exercise makes a lot of sense for the second group.
Forcing the employees to stay until liquidation makes zero sense for the second group. So you need to give the people that do commit at that level a package that more closely resembles a founder.
Otherwise it just distorts the market in all kinds of ways. Nobody would want to work for you until it looks like liquidation is around the corner, which means startups would constantly need to be positioning themselves on the auction block rather than focusing on lasting growth.
In addition, it creates the normal kinds of distortions associated with illiquid assets and immobile people.