While a 4-motor design allows this really cool tank-turn trick, it also prevents torque transfer between wheels / axes.
Some "pedestrian" SUVs today allow transferring up to 70% of all available torque to any single wheel if situation demands. A 4-motor design is limited to 25%.
When you have a truck with 700hp and 800 ft lbs torque, you are only using all that power in good traction situations. I don't think you'll need more then 25% power per wheel with traction in slippery situations.
Also, in bad traction situations open diffs have the issue of transferring all the power to the wheel without grip and much engineering is put into solving this on off road vehicles. A 4 motor electric car solves this while being mechanically much simpler and likely lighter.
I believe that most BEVs are limited by the power the battery can output safely, not by the motor's individual power rating.
I could imagine an EV with a 400hp battery + a 400hp motor at each wheel allowing for 100% of the power to be used at one wheel, where in 4x4 mode each motor would be seeing 25% at max power. I'm not sure exactly how much of a premium you would pay for that but motors are cheap compared to batteries.
Some "pedestrian" SUVs today allow transferring up to 70% of all available torque to any single wheel if situation demands. A 4-motor design is limited to 25%.