I don't really know the trade offs. Maybe they believe a longer short range would be best?
There's a vehicle test track with Ericsson 5G in Sweden (Astazero) where you can stream while driving. I don't know how many radios they use. There are more installations around the globe for showcasing that.
There has been trails of multiple Gbit link to race cars, but that's more or less lab tests. With more cars you will need to share the spectrum.
I just can't imagine anyone being happy with 5G if it doesn't work in your car.