I'd say that the only rational reason would be cost, I can't speak for whatever elon actually thinks. There is a significant difference in product between waymo

I'd say that the only rational reason would be cost, I can't speak for whatever elon actually thinks. There is a significant difference in product between waymo and tesla, i.e. taxi fleet versus consumer product that surely influences these decisions. Waymo are automating a paid driver away, which justifies spending more on sensors. Tesla are going for an incremental path of replacing the driver over time, so that constrains the cost of the deployed hardware. Saying lidar is inferior is just strange. If money, packaging and development budgets weren't a thing then why wouldn't you have it bristling with sensors. In fact you should probably just put beacons in the road everywhere and in every vehicle (maybe on pedestrians and bikes too), then you could solve autonomous driving with very old tech.