CVTs might be boring in cars, but semi trucks don't need to be fun, they need to be powerful and efficient. You've probably seen a semi truck starting from a red light, shifting a million times, barely getting through the intersection before the light turns red again. With a CVT, it wouldn't need to shift at all and it would accelerate much quicker, without any energy lost from shifting.
On the highway, the CVT, in theory, would be more efficient and get better gas mileage, saving the trucking company money. Also, the truck would have more power to get up hills when necessary, and that would lead to more consistent traffic flow.
The only reason I can think of why trucks don't have CVTs already is they can't handle the torque. Once they develop a CVT that can take it, and you know truck companies have most likely already thought of this, trucking will never be the same.
Think about it. Peak torque and efficency at all times. That is perfect for semi trucks.