Because engineering is about trade offs. Why isn't every car body made from carbon fiber? It's lighter and sturdier that alternatives. It's also more expensive

Because engineering is about trade offs. Why isn't every car body made from carbon fiber? It's lighter and sturdier that alternatives. It's also more expensive so you can put it in $60k car but not in $25k car. Radar and ultrasonic sensors are cheap, low power and plentiful. Putting several lidars on a car would be too expensive, would use too much power (less range) and there isn't a supply chain to make 2 million a year just for Tesla (500k cars x 4 lidars per car). It's just isn't possible to put a lidar today on a mass market car and Tesla wants to solve self-driving before lidar becomes cheap enough.