Mistigri, I don't know. I think it's partly to do with teaching methods, with less focus on grammar that, at some point down the line, means that they can more or less handle basic communication, but haven't a clear grasp of how the language works.
I'm not sure what the marking criteria are for A-level or equivalent MFL exams these days. It's possible that it is easier to get on to MFL degree courses now because there are fewer applicants, and I think there are more joint courses than before, so the proportion of time devoted to the MFL is lower than for single degree students in the past.
Also, one colleague at a Scottish university told me they are no longer allowed to refuse candidates for Erasmus exchanges who clearly don't have the required language level. If there are spaces, those students will go. Which would be a good principle if they then didn't hang out with other UK students once they get here.
I teach a French-English translation module for our incoming Erasmus students, and I can see who has learnt the imparfait/conditionnel/futur properly and can therefore translate them accurately and who hasn't.
I've also noticed an odd trend towards presuming that French works the same as English and you can therefore translate word for word.
A surprising number of UK students say "Bon matin!" even though I can't believe they were taught to do so and you'd think they'd have noticed no one ever says that and that there's a surprised reaction when they do.
Or "je suis allé(e) à cette classe" for "I'm going to this class".
It varies from university to university, though, and there are still some really good French speakers. Over the years, I have compiled a mental league table of UK universities which usually proves accurate with each new intake.