I see some mentioned EPA, and that is NOT true!
The U.S. was always home to automatic transmission. I remember before visiting the U.S. firt time hearing how 99% (anecdote) cars have auto. transmission. When I visited first time for 4 months, drove some cars, been driven in many, only one had MT. When I moved to the U.S. I figured that it is a cultural thing. Most Americans look at vehicle as an appliance. Go from place A to place B, AC always ON, big cup holders. After being in the U.S. 11 years, having great job, wife, big house (that American dream except Labrador retriever, but will get German shepherd eventually), I still stay amazed when I go to Starbux or Chik-a-fila or similar place and see more people waiting for drive thru then sitting in the establishment.
I was trying to figure out that, and I cannot explain any different then culture. I am from Bosnia, and before work you do not go through drive thru because there are none except when Mcdonalds came to country, but not sure they still have operating drive thru. Before work, you go to coffee shop (bar actually) sit with friends, drink espresso or turkish coffee, chit chat and you go. No need for big cup holders in a car or similar stuff. You always go with MT because it is more enjoyable to drive, because culture dictates that you drive car for driving not for hauling (kids go to school walking, and for long drives they will just have to suck it up).
So, I remember my father when we would go to beaches in Croatia, we would go with Zastava 101 (Google it) which was predecessor of Yugo. So, I get married, wife is an American, and she is: we need SUV, 7 seats. I am like: noo, I am selling my VW CC and getting BMW 335i xDrive with MT. Of course as an compromise I got X5 35d because life is just so much easier not arguing with wife. But, her point was: what if we need 7 seats when someone visits us. First of all, 4 of us used Zastava 101 to travel, so whoever needs ride from f.... airport can survive two other people in my X5. Unfortunately, my logic did not work with my wife. Of course, since i got X5 I never opened those two [removed] seats, and I do not have space for spare tire.
She of course does not know how to drive MT, and her whole family is like: from point A to point B, and car is necessary evil. Compare that to Italy for example where someone drives Alfa Romeo that is in shop every month, but if you ask them about issues they will say: that car breaks because it has character. They blame themselves for car issues.
To answer OP, I would not only mandate MT, but would make cup holders as unaccessible as possible. Maybe we make more people sitting in Starbux making small talk, and help with obesity epidemic.
