Since the 1960s America has taxed light trucks being imported. Because America didn’t have to build light trucks to compete internationally they lost the international market on light trucks. Now nobody wants to buy American cars and trucks because they are not as good as what others countries build. So now America has put up high tariffs to make itself even more isolationist, since they can’t compete.
The laws state that regular cars need to meet many regulations, while trucks are exempt from them. So trucks got larger. And without competition from foreign trucks, they got even larger.