There is a bias in this article and that is the context of time. Over time there will be less and less software engineers at the top of this list as software engineering becomes more common field of study. If you look at the people listed, they were people who set up these companies not to make money. I am not saying they are not interested in money, but if you were someone interested in mainly in making money within a reasonable time frame and you were intelligent at the times Google, FB and others were invented, building these companies would have not been the easiest way to make money at those times (dot com bubble etc). These people started these companies due to an obsession with the problem, the need to make a change etc.
These companies have grown to be insane empires, not because it has been software engineers running them, but software engineering is a new field that greatly impacts the world at this time and they are the people that solved the harder mainstream problems at the time. If this was in the industrial age, we would see more blacksmiths and manufacturers and railroad builders on the list, than farmers or accountants or whatever. It is a mixture of time, depth of problem and an obsession to solve it. Not that there is something intrinsically special about software engineers