The team behind it - these guys have each built multiple successful companies with exits or massive profits - together with the YC spotlight. You're right that being in YC alone won't cut it but as we've seen it definitely amplifies the power of a great team.

The YC spotlight is particularly perfect for this concept because of demo day. They might be the only startup that can get all their most important and prominent target customers (and thought leaders) in one room, very shortly after launching.