* Banks don't want to do business with these particular people because they know them to be a bad business risk. They often know, via credit reporting methods, that the specific individual human standing before them has a history of cashing bad checks/committing fraud/whatever it is. Therefore, they decline to work with that person.
* The people who are bad risks for banks get rather tired of dealing with banks, both because constant rejection is tiresome and because bank employees make it very clear (though unspoken explicitly) that they are persona non grata there. By contrast, the people at the check cashing shop treat them better, so they would rather take their financial business there.
I get why you want the explanations and not just "for reasons", but both of these points are quite clearly spelled out in the article. So I don't really think the author deserves the grief you're giving him in this case.