Or that the employees might have changing life circumstances any time in the 10-15 year future. Find a partner that changes your life needs around working life or living location, have a kid, need more or different housing, have medical issues, have family with medical issues, etc and you're sol.
ps -- a16z funded a company that, as an A round, refused to disclose outstanding shares to value my option grant and was already on the brute force 15% of comp is bonus that you don't get if you aren't there in early April every year retention ("bonus") plan. It may be unjustified, but with some other stories I'm not a liberty to disclose, they seem very employee unfriendly.
Most option plans are employee unfriendly. And "This incredibly employee-hostile clause will force us to be more honest with employees, which makes it employee-friendly" leaves a bad taste in my mouth. It might work as long as the original founders are in control. They will be in control ten years later, right? Right?
My spouse worked 13 years at what was a startup-with-traction when she started there. Last year, they were bought out (public-to-private by a hedge fund). A week later, she was sent packing, along with a lot of the "old-timers". That's not even getting out of options (although there was some of that). That's a simple purge. Purges happen.
When you ask employees to commit to ten years to get anything equity-wise, you're exposing them to tremendous risk. You're hampering their careers. You're exposing them to the risk that you'll take a down round three years down the road and their options will get diluted into near-worthlessness. You're exposing them to the risk that your business will be wiped out by a competitor, or put on the road to obsolescence by technical advances and market trends.
For a 50% bump? Screw that.