We don't always just close the thread.
We clean up and reopen many more than we leave closed.
Sometimes a very long thread has so much to clean up that is not feasible to spend hours on it.
Remember we are all volunteers and have limited time to spend on the forum.
If a rules violation is reported immediately, instead of members quoting, requoting, responding, chastising or just posting a popcorn smiley waiting and watching for the train wreck, the problem can be dealt with immediately and quickly.
But when a report comes after pages and pages of egging it all on, it will take more time than we perhaps have at the time.
Remember that you can edit your own posts. If you feel that you have hit the "submit" button before thinking, you can always go in an edit it. Just hope no one quoted you.