Just as a point of order, in a pub, the mark up (say) on a bottle of beer is fairly hefty. A vast amount of what you're paying for is gas, electricity, rent, staffing costs. And every time someone's having a diet coke, they're not haing a beer, so to price them much below makes no sense. I think that, for a long time, people did try and keep the price of soft drinks lower cos it encouraged people not to drink and drive, but with the the cost of alcohol shooting up, and increasing numbers of people drinking less, pubs have had no choice but to make soft drinks more expensive. I can't tell you how often I've heard that postmix costs pennies, that may be true of the product, but all the other costs are still there.
Back on topic, I have literally no idea how Clinton Cards didn't go bust years ago. I've always assumed it was a very elaborate and well-concealed money laundering operation. Apparently not.