Well theres quite a few reasons.
First of all- if I am one of the cases where things get harder towards the end, my body may physically not allow 8 cm due to tightness etc. Although I will say that Paley and his team sort of misled me, saying no one had ever not achieved 8 cm who wanted it, but then after surgery the PA was basically saying how if I develop issues keeping my legs straight etc that they would need to stop lengthening me.
A theoretical reason is the nail stopping to work, which happened for another LL'er at 7 CM.
Then theres proportions, which I might find to get a bit off, although its hard to tell when not filled in by muscle.
Lastly theres the fact I want to recover in a reasonable time frame and get back to my life- I'm already sick of this lifestyle/the pain/limitations etc. and there are also people who depend on me to an extent back home, and I'll have been away from being full time with my business/focused for awhile and really will need to get back to that.
Who knows, maybe there will be no more setbacks, things will improve, and at the last ten days I'll decide to keep going, but currently I'm certainly open to stopping at 7 or so.