I can answer that question.
I have seen the same figures, basically, since 1993. Indeed I see that the number of people who take English classes has always been lower. In a previous job I managed a language school and it was the same thing.
Here we always start from the premise that the francophones are more bilingual and that consequently they need less second-language training. As I said earlier, we do not give the members tests. Consequently, we don't know what the members' level of bilingualism is, and which ones need training. That data does not exist and we start with that premise.
Given the historical data not only here, but also elsewhere, perhaps the issue of bilingualism is a factor. I do not have a conclusive answer.