This question has been asked and answered recently by someone else, but: Quora is agnostic about a banned user’s questions (or answers for that matter). Even if a user is banned for troll content, it is not assumed that all their answers are trollish, and those answers need to be reported, to be evaluated for collapse or deletion, separately.
That goes even more for questions, which once written belong to the community (to be reworded at will).
Yes it’s more work. I’d rather that work than the alternative over indiscriminately removing anything ever asked by a user, and making all the answers anyone has ever given inaccessible.