Founders are committed and in for the long haul, and either make a lot of money or none. 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…
You retain employees who might have been great from the zero to 50 stage but not as well suited in the 50 - 5000 stage. But their incentive is to stick around or give up potentially millions in equity that they busted their asses to earn.
Checked out employees aren't doing anyone any favors. You might say you can fire the person or put them on a performance improvement plan but this is easier said than done - especially if it was a key early hire.
I've seen this in many SF-based companies.