I believe they said that LIDAR was so low resolution and was giving so many false readings that they had to give it up when using it in the real world (non pre-mapped cities like some other companies).
Another argument is to not fuse the data. Just keep it as a backup decision maker akin to how Aviation systems are designed. If both systems agree, then you have additional reliability. Would love to hear from someone who's worked on these kinds of FSD systems.
Andrej covered this in a previous talk. If both systems agree, then nothing would be different if you did not have the 2nd system. If the systems do not agree then you ultimately still have to pick one in most scenarios.
IE if you are travelling down the highway at 80mph with a car close behind and your lidar+radar system says there's an immediate obstacle but your vision system says it's an overpass, do you emergency brake?