They promised a feature that would enable waves to be embedded into normal web pages. This would allow me and others to collaborate on waves, but for the results of our work to be publicly viewable in a read-only fashion.
Because they never delivered on that feature, I never actually used wave much. There was no reason to because as a private-only space it was just a weird chat room / document.
Even if someone else doesn’t think that feature was important, I still think their biggest failure was simply not continuing development. They released it and hardly updated it at all. Even if it wasn’t getting traction out of the gate, they were on the right track. They just had to keep iterating and it would have ended up in the right place. They just gave up almost immediately.