No sure why they just chose trucks. You can probably ask an LBJ or UAW historian why.
North American built truck can be foreign and domestic make and it really isn't protected just US trucks since any make can build a factory here and avoid the tariff just like Toyota and Nissan did. What the tariff is protecting are the American factory jobs which was its intended purpose by the UAW. Although one can also say that making a truck in Argentina or Thailand protects manufacturer from having to pay taxes, higher labor wages, labor health insurance costs, as well as other safety and environmental regulations like manufacturers do in the US.
