The thing with really long lift shackles is geometry. If you think about it, when a leaf pack compresses it essentially is being stretched...the longer the shackle, the farther the leaf pack stretches. This increase in stretch really stresses leaf packs out, and stock spring packs that have already been around for 10+ years succumb to the stress and eventually invert.
Ergo.....monster buck teeth lift shackles kill leaf springs quickly.