I think SYNC implies upload/download settings etc. via iFly servers over internet to sync settings across devices. Would not be done in flight. More of a settings function. Requires network with internet connection to talk to servers.
SHARE on the other hand just uses network for peer-to-peer direct sharing of plan etc. (no internet connection needed)
So likely why made made sense to bury sync within settings but share more in flight-plan area for use while operating.
That's my guess and I think the distinction/separation makes sense if Im stating the distinction correctly,