I would wager that's because there isn't a lot of existing silicon that fits the bill. What COTS equipment is there that has all the CPU/Tensor horsepower these systems need... AND is reasonably power efficient AND is rated for a vehicle (wild temp extremes like -20F to 150F+, constant vibration, slams and impacts... and will keep working for 15 years).

Yea, Tesla has some. But they aren't sharing their secret sauce. You can't just throw a desktop computer in a car and expect it to survive for the duration. Ford et all aren't anywhere close to having "premium silicon".

So you're only option right now is to build your own. And hope maybe that you can sell/license your designs to others later and make bucks.