Besides, credit histories often have incorrect information that needs to be corrected, and often creditors will cut you a deal or just be nice ("goodwill adjustments"). Blockchain history is immutable, so how do you handle this? Sure, you can write something to the blockchain that amends an existing entry, but the existing entry is still there to see, even if it was erroneous. I would bet that some lenders would use "has more than $SOME_NUMBER amended entries in history" as a negative signal, even though it's not necessarily fair to characterize them that way.
Hell, negative things on credit reports (in the US) disappear after 7 years. Sure, you can tell lenders to disregard negative things older than 7 years, but do you really expect them to do that?