Trucks are just an illustrative point. Substitute for whatever trivial thing it is that people like and would not be willing to give up. {Beef, air travel, fast fashion, 69 degree interiors during the summer, etc.} Each one of these things only contributes a little on their own but if you add them all up it sums to a large fraction of overall US emissions.
Also not sure where you got the 3.7% number, but light duty trucks overall contribute around 10.4%. This includes some fraction of SUVs (those with truck-like drive trains weighing over 6000 pounds GVW) and minivans.
That being said, decarbonization of the truly necessary energy consumption is also a requirement, and that is expensive too. You need to convince people that they should want to pay for it -- no the billionaires cannot pay for the whole thing, for inflation-related reasons that are too complicated to get into right now. (The basic thrust of the argument is that US construction and industrial capacity is already highly utilized, and that allocating more workers to decarbonizing will necessarily drive up the cost of everything else, regardless of who nominally pays for the work.)