Do you have any pics of this most recent trim?
While yes, in general, TBs have thin walls. But I'm quickly learning, the fastest way to grow a thicker, healthier wall is to shorten the toes. While I won't and cannot explain this part, my understanding is that laminae (the main ingredient that makes up your horse's hooves) is a lot like stem cells. It goes where it needs to go. In a normal, well trimmed hoof, the laminae is free to build up the hoof wall. In a case where the entire foot is stretched forward by long toes, flares, or otherwise crap trimming, the laminae goes to those areas to compensate for the damage and the overall hoof wall integrity suffers. Not saying this is what's going on with your TB, but as someone who when through 7 farriers before giving up on one that could properly trim, my suspicion is your horse's poor feet are partly due to how they are being trimmed. Pics would quickly help determine this.
You just have to see your distance...you don't have to like it.