1. While stereo depth estimation would work in theory, none of the self-driving cars actually have camera configurations that allow for stereo depth estimation (see here: https://electrek.co/wp-content/uploads/sites/3/2016/10/tesla...)

2. Stereo depth estimation is quite unreliable in practice because it requires you to match up pixels between the two images very precisely (1-2px difference can be a large disparity in distance), so it is not reliably used.