But given that a large part of undocumented immigration is due to people overstaying their initially legitimate visas (essentially deciding to not go home as required), the normal visa program has to remain closed, as it has been for a long time, to anyone who would have a high probability of benefitting from remaining in the US. 

Based on a government report issued in Feb. of last year, approximately 415,000 people whose visa was supposed to end in 2015 have decided to stay in the US. That's just for visas expiring in 2015. Presumably a similar story exists for every year. It adds up fast. 

This is a judgment call that State has to make on every visa application, and given they can't know what is in someone's head, they have to be convinced by objective data that the person would not benefit nor want to stay here as compared to returning home. 

This gentleman can't satisfy that criteria. So he doesn't get a visa. It's not political.