They could've done a lot more if they were more focused, but that's not really how Apple works. They don't really research based on current technology, they like to spend time & money what could be invented. They even investigated things like "spherical wheels" [1]:

> Apple even looked into reinventing the wheel. A team within Titan investigated the possibility of using spherical wheels — round like a globe — instead of the traditional, round ones, because spherical wheels could allow the car better lateral movement.

[1] https://www.nytimes.com/2017/08/22/technology/apple-self-dri...