The premise here is that extra money over the "financial independence" limit has a relatively low impact on the recipient. It's obviously not zero, but that extra money given up by the founder will have less of an impact on them than the impact it will have on every single employee that gets part of that money. To make up an example, if a founder gets $500M instead of $1B, but 500 employees get an average of $1M each, then the impact on every single employee is probably much greater than the impact on the founder (multiply that by the number of impacted employees and it's an even bigger difference).
He's referring to the marginal utility of money [1], where $1 means more to a person with $100 in the bank than it does to the person with $100M in the bank.