Yes, it's very obvious why Proton isn't on the list.

Protons cars simply could not meet the US Safety Regulations. I'm not talking out of my ass, this is a fact. No Protons have been sold there since the Saga 2 decades ago I believe (which was before they raised their safety standards).

The pre-facelift BMW 7-series is one of those cars which is very good inside but ugly outside. I guess the Time people considered looks to be a major factor as well. Nevertheless they were honest enough to include many of their own national cars.

In my opinion the Ford Model T shouldn't have been in that list though, it was a major breakthrough! Same goes to the Chrysler Airflow.