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.
I'm a computer security researcher. At some point I posted a public key for people to send me encrypted email. Nobody ever did and at some point I lost that private key.
Point is, key management is hard problem for big corporations with dedicated IT staff. Relying on normal people to be able to do that is just insane.
I'll give another example. My medical practice tried to do GPG encryption in a shared DropBox folder. Within the first week, someone decrypted half the files into the same shared folder...
It was all just a test with non-critical data, but the test was a total failure. And that didn't even get into key-related issues.
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.