I've worked on projects in this sector before, and it's a common story to others - client cuts cost as much as possible, until the risk of an inferior product has grown too high to handle. It's a race to the bottom, and security rarely comes into consideration outside of a basic pen test being mentioned (if it happens).
Still, I'm quite annoyed at the lack of follow-up against what is blatant bullshit from BA. When your business is so heavily reliant on taking payments online, their security procedures should be airtight. I can understand that it's quite a clever hack, but it's security 101 to know what third-party code is doing on your server.
The fine is good, but it would be nice to enforce rules where a company caught in a data breach has to accept liability and not contest the severity.