Wolf, Ubiquitin, etc.: Just replace the words “Sinai” with “Arvos Moav” (which everyone, except the Rambam, agrees to). Then the question still stands.
Talmud: In short, he held that it was a Busha to say like the Geonim and that Chas V’shalom that we could forget so much. He says that Pratei Dinim weren’t given to Moshe Rabbeinu. What was given was the text of the Chumash, a few Halachos L’Moshe MiSinai and Peirushim Hamekubalim Misinai, and all of the Klalim (I think if you count them you get like 365 or something). Then it was up to the Chachamim in every generation to Darshan out according to the rules and vote. Thus, the lack of Machlokes before Hillel and Shamai wasn’t due to there being Nevi’im who could Pasken, it was due to the fact that we had a Sanhedrin and thus could reject certain Shittos with finality. Once we lost that, we could no longer resolve disputes as both ways of Darshening are equally valid. Thus, every Machlokes in Drashah is Eilu V’eilu and we lost the way to reject minority Shittos, thus the Mishnah and Gemara and Midrishei Halchah are full of disputes.