The pimps keep advertising their services, we keep marking those messages as deleted (within seconds even), yet the advertisement is sometimes retained for hours or days.
This "oversight" or "design flaw" allows these advertisers to profit, even if their user account is deleted, since Y!A continues to advertise their services for up to hours.
I understand (or guess) that a copy of the question resides, formatted for quick search. And apparently, that "copy" does not point to the original question, and does not reflect its deleted state.
Why cannot the deletion process delete *all* copies, every time? This would be the lowest overhead.