There have been some service issues that turned out to be caused for what I think are pretty good reason on various airlines including BA, most of which have been medical issues on board that required a number of crew members' attention.
I'm certainly not saying that this was the case on the OP's flight but in my experience in a lot of cases crew members are quite discreet and simply said they became short staffed (in one of the cases the ill person was actually a crew member - so that would be a rather direct cause) but they told me why when probed a little further.
In some others there were things like major spillage that needed to be cleaned up before someone slipped over etc.
I'm not justifying bad service but there could have been reasons behind it.