Probably because zo widens the face. You jaw is a fair bit narrower than your zygos. No point in widening the jaw only to end up with it being still narrower than your upper face (for a man at least).
Yeah, my Jaw width is the real issue. He only told me about ZO because I mentioned my nasolabial folds and he said a ZO would strech the tissue. I also pointed out that my Zygos are already broader than my jaw, he said that it's a missconception to think that it would widen the entire face rather than it would create a shadow. I don't know how much sense that makes.
I'm really disharted right now to be honest. I actually wanted the Le Fort. I also went to a orthodontist, who told me that my bite is nearly perfect. I don't really know what to do.