Oh.... OK.... On the ground surface, walls don't look too long, except perhaps a tad at the quarters & maybe heel(s), but those very stretched toes(well, entire front halves of feet) haven't been addressed at all it seems. No wonder the crack has been 'incurable' if flares don't get addressed. You can learn the whys & wherefores of hoof balance pretty well at Equine Lameness Prevention Organization
The sole pic I've drawn on shows approximately where I'd 'back up'(very strongly bevel) the walls back to, approx where they should be if not flared. The pic of hoof on the ground shows approx where it appears the wall should be if strongly attached.
I also think it's important to dig/clean out cracks as much as necessary to remove diseased tissue, as it's next to impossible to kill the infection if not - mind you, if flares were addressed adequately, there may not be much more to resect. Untreated infection is also a common cause of perpetual cracks too.