The trucks are driving between relatively fixed points, so it's a simple matter to build CNG stations there. Plus, the cost of a battery scales linearly with the capacity of the battery, while the cost of the CNG tank scales the square root of the capacity. Batteries are also heavier per unit energy, which reduces the truck's legal payload capacity.

So that use case has a strong argument for CNG.

Weight doesn't really matter for a personal automobile, and you can't (easily) make the tank big enough to argue that a large tank is cheaper than a large battery. It's true, but costs unrelated to tank size are still important, and the bigger issue is that the range sucks unless you give up the entire trunk (since you can't make a CNG tank flat (like Tesla) or T-shaped (like GM).