MasterCard gets hacked (or someone internal steals the data, same effect). Now someone can imitate you to MasterCard, buy expensive stuff, and blame you.
Worse is if everyone uses the same hash as MasterCard. Say, the IRS, or the passport office, or the police. That's outside the scope of your question, though, which was if only MasterCard had the hash.
That requires effort. A seize order doesn't, and the cops have already adapted at using third parties like Google [1] to get access to data they should not have in any decent legal system.
Worse is if everyone uses the same hash as MasterCard. Say, the IRS, or the passport office, or the police. That's outside the scope of your question, though, which was if only MasterCard had the hash.