Perhaps I am misunderstanding what you're proposing, but If you moved all credit info to a blockchain, then everyone's info would be public. That seems to be opposite of the goal, so how is that better?
Also, the credit agencies, for better or worse, weigh the different factors in a credit profile, to provide an approximation of an individual's credit worthiness. This information from a credit bureau is solicited by many lenders who are providing the credit.