> Why would money be the only value, that is a really sad view on life.

Good thing nobody said that.

> The developer gets joy and gratitude,

Your average free software doesn't get very much joy and gratitude back from users either.

> they can live a happy life. Why bring money into it. Money does not make happy.

If the implication was too subtle, the idea is that when you spend a lot of time making something valuable, it should go towards obtaining food and shelter and the other benefits of a living wage.

And those things do make happy.