The tall deck of the I6 is part of the reason we have that stupid split axle design. And take a look at the torque. It produces a little more, and it produces at a considerably lower range. Low-end is where you want it for hauling applications, the motor doesn't mean squat if it can't get the trailer moving in the first place.
OHC does have its merits. You don't have to worry about lifters if for some reason you're against a technology that's been proven and built upon for decades, and with proper aftermarket support things like hotter cams becomes easier to turn from idea into completed project as they're usually easier to access. But it just isn't for all applications.
As for manufacturing cost, some of that gets shoved onto the end consumer so some portion of it can be subtracted. As far as I know, the other versions of the Atlas are still in production, or at least survived the cut longer than the 6 cylinder. There's more "play" available as the engines are smaller. The I6 weighs over 400 pounds and is fairly long compared to a V6 design (trading length for width, which there is plenty of in a truck).