So why is that when.....?

Nothing happened to their crappy answer because you didn't report it. Replying to answers with your question, regardless of the reason, is considered chatting. It's a comment directed at one person... chat. What you should have done is not responded, and just report the answer. It's not even likely it was the person who gave that answer who reported it. Even if they did, generally 2 or more people need to report for a question or answer to be removed. I'm sure that answer would have been reported by a few people had you done that instead.