Likely the weight and classification of a truck is why it doesn't have a gas guzzler tax.
My opinion: As Ram added the 35in tires, the suspension components, the spare 35in tire, then the hellcat engine, they realized they probably had like 400lbs of payload left, without options. Now add in the larger bodywork around the tires. They had one heavy, heavy truck.
Add in the huge HD axle.
They also had a big honkin truck flying up and down the dunes, way heavier than ford's aluminum body - and now needed a beefier frame. Now you need beefier brakes to stop the damn thing and restrain the 700hp!
The extra weight had a benefit though, it's probably way easier to keep alllll that horsepower on the ground now when used in combination with their 4x4 system. 700hp is no joke.
It's long-ish, it's heavy, it's got a lot of rubber and wide tires on the ground, it's wide too. There's a bunch of things working together to make that horsepower manageable. It's also turning those wide 35in tires.
I suspect Ford has walked away from "This 3.5 ecoboost in high output trim is allll the engine anybody could ever want" strategy and has a V8 ready.
I saw a video of what someone believes is a V8 test mule rumbling away.
I do wonder if they will be able to get 700hp out of that engine,
and how they get it to the ground. I'm thinking they will use the "Torque management" software strategy, and end up with a competitive 0-60 number due to how light the truck is, vs the raw brute force of the 700hp hellcat.