I didn't. Please read the multiple qualifiers I added to that phrase.
>> If you collect enough people, with sufficient heterogeneity, you will find that the GCD is always financial self-interest.
What that means is that if you scale groups of people too much, the only common interest you'll find among _all_ of them will be financial self interest. Hence GCD - "greatest common divisor". Of course people do things without monetary incentives. But these interests don't overlap within a sufficiently large and diverse group of people, as much as financial self-interest does.