It is something I could discuss but I think that this is an MP's right, just as voters have the right to elect the representative of their choice without concern as to whether or not that person is bilingual. I should also note that it is up to the Prime Minister to choose ministers from among his or her MP's. This is a difficult question, in my opinion.
There is another factor that I noticed when I was a journalist. Often, the language of the answer is chosen according to how the speaker wants the answer to be shown on television. That's a political reality.