For some a tiny phone screen is not a possibility. Also phone games are not equal to steam games. And some would not want to own a Steam Deck or Switch and pack it around with them in case they need to charge. It certainly isnt a priority, but if your car has a computer capable, why not?
The article says the TVs still capture input and do recognition from external sources so using an external device is not helping.
Edit: Unless your tv is not connected to the internet.