A lot of the problems John mentioned (camera jpeg, latency, real time decisions) have been worked on by comma.ai for many years. He could have just used their stack and build on it the general learning parts that comma is not focusing on.

Carmack himself has done a lot of work on end to end latency, during his time at oculus.

This is Carmack, who builds new things. He built one of the first 3D game engines based on the hard math.

Reuse is not always necessary - sometimes things are just done for fun and exploration, not for appeasing thirsty VCs and grabbing that market share.

And plenty of other people.

It's still a lot better to really learn and discover it yourself to really get it.

Also it's hard to determine how much time someone spent on particular topic.