Because many times topic creator deletes the whole thread and we can not track it easily.
User's can't delete topics.
what do you mean? I mean if I create a thread and delete it after a few hours/days then all posts on the thread will have vanished automatically.
You can delete the topic you created.
Below is the last topic you creahttps://bitcointalk.org/index.php?topic=5255788
Click on "delete" button and see what will happen.