Neither, but my coworkers are apparently unable to carpool to a lunch spot 5 mins away that we visit every 2-3 weeks without setting nav first.

Once the city you live in gets large enough, memorizing the routes just becomes a non starter. I have my route to work almost memorized but due to construction or crashes it changes so often it is hard to cement it. (Seoul)

Because the traffic isn't known to you but it is to Google. I could take two routes, one is faster depending on circumstances, and Google knows those circumstances.