I don’t know why you say that is so. Say after 6 months you have a relapse. You pick up the phone and tell your sponsor. He/she will encourage you and talk about why you did it. That should help you understand your impulses better, which will help you break the habit for good.
Or, say after 6 months you feel like you are going to have a relapse. You pick up the phone and call your sponsor. He/she will encourage you and try to talk you through what you are feeling, so that you can let the feelings subside and not do the act. It won’t work every time, but it will help.
The reason most people don’t get a sponsor is because it is hard to share you weaknesses with another person. That’s why anonymous groups work well – comfort of strangers.