Because sync for lemmy is still in beta. If you don't want to use a beta product then don't and wait until its a bit more fleshed out. As others have said, it's coming just give it some time. LJ is doing this solo afaik.
Also, the reason for the public beta is because people practically begged LJ for it. We actively told him, "We don't care if there are bugs or missing features, just gimmie now!"
Hmm, I agree that it is rather odd submissions weren't included with the beta. Feels like danging a carrot, but it is what it is I guess and JL is working on it. What's even more curious - is why we haven't received any word on the "sync" feature that is also missing.