When people relapse week after week, and post about how terrible they feel about that, my first thought is to want to say "if you could stop for good right now, you would. There is a reason why this keeps happening." I don't know what the reason is, and it's clear from their pain-filled messages that they don't know either. And yes, it's likely to keep happening until they are able to figure that reason out. But eventually it will happen. The penny will drop. Perhaps they'll see a therapist for help, or someone at an AA meeting or on here will share some of their own experience that's so familiar a light bulb will switch on. Until that happens, all we can do is offer our support and reinforce the message that the goal of sobriety is worth the struggle.
In my case, I would constantly ask "why do I keep doing this despite knowing how terrible I end up feeling", and the answer turned out to be "I keep doing this because of how terrible I end up feeling." Doesn't make any logical sense, but it's how people's brains can work (out of our awareness). We often find ourselves in situations that are familiar, even if what's familiar is painful. Working with a therapist to figure out my own role in creating those situations, and finally dealing with what was in my past that was leading me to do it, has made all the difference to me. My last drink was in May 2015, and I will never drink again.