Your answer could easily have something to do with the following.
Currently, borrowing money from a bank is really the creation of new money. The bank doesn't lose anything if you default on the loan, since it was a creation of new, and not really a loan.
The bank is enriched beyond what they deserve by the so-called loan and interest payments received for nothing.
A default blockchain currency could easily use separate blockchains for every bank. This would cut down on the big blockchain ledger of Bitcoin. It would also allow the creation of new money to be hidden in the scripting code of the program. This would make it harder to find for the people who wanted to prove the fact of bank enrichment for nothing.