You could understand BA wanting to avoid confusion in the majority of the public by hiding this information. However, it could easily be added as a bit of random text on the booking page, e-ticket receipt etc.

The especially silly part is when BA have consciously decided to hide the information on booking, but then expect you to somehow know it if you want to take advantage of one of the offers; e.g. "offer only valid for J,C,D fares".

ISTR it being mentioned on a thread similar to this one that BA are considering showing the info in the future.