I think Detroit and other manufactures are fearful of automation. If you ask them what the future looks like its driving assist technology. Fully automated driving kills the emotional experience that is used to sell cars.
The bigger issue is that autonomous cars make it extremely easy to massively boost utilization: driver assist still means your car sits at home, work, etc when not in use. This in turn means more cars are required by society. Autonomous cars can achieve much higher levels of utilization. This is the real reason legacy car makers don't want fully autonomous vehicles.
Cars that do 400 miles a day will reach 200'000 miles within ~1.3 years. Usually most cars are fairly low value by then. They would reach 400 miles by being on a highway for ~6.5 hours/day, which is fairly reasonable to assume.