That's probably because they haven't experienced enough things in life. This world is huge with so many different opportunities.
People who appear dispassionate, are not always so. There are people who are passionate about serving their family. Or maybe some sport say football. They have to find a way to channel their passion to their careers. I admit passion is not enough, you need talents but that's again about channeling passion in the right way.
Of course, there would always be some people who would be physically (biologically?) incapable of feeling passion. But I don't think that is the norm.
