It's really a question of timeframe. You are completely right that we theoretically only need two cameras. But by limiting yourself to 2 cameras (or cameras + other non-lidar sensors) you're just making the problem a lot harder for yourself. That's a lot more computer vision tasks your research team is going to have to solve, a lot more models to develop, a lot more failure cases (less redundancy).
Some of these vision problems have uncertainty over how long it will take to perform at human-level accuracy. Whereas if you go with lidar, I don't think there's any doubt the costs will go down. IMO on the market, a $5k sensor cost is also nothing if your car is actually fully self-driving.
Some of these vision problems have uncertainty over how long it will take to perform at human-level accuracy. Whereas if you go with lidar, I don't think there's any doubt the costs will go down. IMO on the market, a $5k sensor cost is also nothing if your car is actually fully self-driving.