They probably started without lidar due to the cost (Tesla is one of few companies actually selling cars to customers, who are sensitive to price). The price of lidar has come down, but I would guess it requires a fair amount of expensive rearchitecture to add it in now, and they haven't bitten the bullet yet.
He was asked point blank if they would use Lidar as Tesla even if they were free... and he said no. In their opinion it's simply not the right approach to generate photons and read them as they come back. It's preferable to simply read the photons that are already coming in.
Then why have lidar? If it's only purpose is to agree with vision or you just discard it, then why even have it?
You might want to not have sensor B to lower the cost (as I suggested). Or you might want to have both sensors A and B because the provide some synergies (as gkop pointed out, better range of view, increased confidence, etc.). But it’s definitely not enough to just argue that the sensors may conflict.
I'm almost doubting my entire knowledge in the field now when all of a sudden everyone just accepts that "sensor fusion is hard" statement.
I just think there's more to the story than we're getting. Impossible to tell for an outsider though.