I loved this post. Human behavior is inexplicable sometimes. Why does my friend with COPD still smoke? And also complain about her breathing problems? It goes beyond eating; most of us repeat counter productive behaviors despite vowing to stop.
I read a meditation during Lent which cited a Bible passage that asked the same question, so 2000 years ago people were pondering the same problem and not much has changed since. The heart wants what the heart wants, I guess, and the head can't always sucessfully stop it.