Why can't many loans go to the bank by themselves or the amount is low, and the same qualification can be found by an intermediary or the amount is high?

This is mainly due to information asymmetry between individuals and institutions, and other factors. Information asymmetry is mainly because individuals don't know the standards of bank audit, but intermediaries know that at least when filling in information, the same qualifications and different descriptions are very different. There are many other factors. For example, some intermediaries are willing to participate in loan risks to get opportunities for bank cooperation, some intermediaries help you play some hidden rules and provide false information, but they just don't tell you, while others collect your past credit ratings and provide them to banks in addition ... This is an era of detailed division of labor. If there is no such professional level, why exchange value?