The article sounds like the reporter heard a soundbyte about google's typical four year vesting period, and then did zero actual research into what that means.
I left my last job pretty much on the day of my 4 year anniversary because I'd otherwise be taking a 25% comp hit in year 5. It's definitely a thing.
After 4 years, unless you got refresher grants, your compensation is just your salary, so you effectively make less money than during the first 4 years. At that point the incentive is to move to some other company and start the 4-year clock again...
Thank you for the explanation ;)