I just came across this article (read it in a private window and it should be available for free) which explains that pretty well.
It comes down to:
Whoever you bank with, you’ll be paying them a lot of money. It might be through opportunity cost, or fees, interest charges or transaction charges. You are still paying. On that basis, why pay for poor, impersonal customer service? IT systems that fail. Branches with long queues. Telephone call centres that frustrate. Arduous processes to borrow money when dealing with a short-term credit crisis of your own. I value my time, as that’s what I am short of. I also value the ability to do things with my money when it is not in the form I want.
There is also confirmation in the article that you get a golden-bottle debit card.