You seem to have two unrelated questions mushed together here. Good security technically has nothing to do with customer retention. It's how the brand manages that security for their customers, and gets around it when needed, that causes the potential issue of losing the customer.

Your experience was with customer support, probably first tier. They couldn't provide you with what you needed and I bet they didn't escalate to tier 2 or 3 to see if a supervisor could come up with a work around. That is their problem, and their processes. But these people weren't managing security. In fact, I'd be surprised if they even had access to the information you needed. In companies that have a clue, the front line employees aren't able to see that information without a mask.

But your point remains. It was not good customer service that you received, and you got a bad impression of their processes and security regulations. Hence, their "good security" lost them a customer.