The success of Linux is in large part due to its open source nature. Why do you think people have been willing to give up so much time without financial reward?
In many ways, I actually think the real idea of open source is for it to allow everybody to be “selfish”, not about trying to get everybody to contribute to some common good.
In other words, I do not see open source as some big goody-goody “let’s all sing kumbaya around the campfire and make the world a better place”. No, open source only really works if everybody is contributing for their own selfish reasons.
Now, those selfish reasons by no means need to be about “financial reward”, though.