Ultimately one has to assume good faith first.
It costs bank to print and send these cards. Thus they wouldn’t do it if the costs did not outweigh the benefits.
Knowing how much information Monzo shares with customer (future Bacs, future direct debits, push notifications for everything), it should be clear they really couldn’t share why at the time, or even indicate that they cannot share details why at that time if they are able to disclose it in the future.
Obviously, inconvenience of the customer is considered. Because one doesn’t intentially piss customers off.
It strikes me off how emotional response is in the original post “inconvenience to update card details” and “I am entitled to know more”. I don’t believe either of those exclamations to be true - using a password manager that can autofill details is trivial, including copy&paste details from Monzo app, or simply use apple/Google pay at checkouts which is more secure. And they did disclose everything they could as much as they could at the time, including stating so.
The initial messages of this thread come across very brass.
Is there lack of trust in banks, and communications/actions such as these such that statements “we cannot tell you why” are perceived in bad faith? It feels like OP, at the time, believed that Monzo is intentional hiding something or cannot be bothered with details.
“We wish we could tell you more, but we cannot. This is in order to protect you or any other people affected but the very same or similar fraud. Our actions intend to prevent this fraud against not only you, but also other customers off our and other banks.” - would wording like this be better?
Just like fraudsters do not disclose their methods and how they obtained leverage, so does fraud prevention teams do not disclose the exact details of how they detect / prevent / circumvent fraud. I can see how MasterCard for example can keep stolen card details active and approve transactions for them, to catch and figure out who the criminals are. A digital booby trap. But this requires information imbalance as surely some fraudsters have legitimate accounts to snoop on the current security practices of every bank.