Clearly flagging doesn't work, or at least doesn't work fast enough in the current conditions. Plus, people run out of flags (and downvotes).
Right now the situation is farcical. Although enough flags will delete a question, there are so many spam posts and they arrive so fast (they come at the rate of about one every 15seconds now) that it's not possible for a post to accumulate enough flags to close.
Even if the spam poster is banned, another account under a different username is immediately created to keep the wheel moving.