Well you know a Simulator is supposed to be as realistic as it can (so SCS did already an issue allowing people to disable the speed limiter) but basically what you are saying is
People shouldn't play Simulators as they supposed to be played because driving without a speed limit with a truck is basically just ruining the whole Simulator
for an example:
Hey let's buy Car Mechanic Simulator and repair planes there
Why would a car mechanic repair a plane?
the same thing goes with: Why Would a Truck Driver drive over 90?
Just tell me When did you see a Truck in real life going over 90?
because if every Truck driver would drive over 90 with the Truck it would probably wipe out the half of the humanity by now because the accident percent would increase way way higher and everybody would be scared of crazy Truck drivers
and the only thing i can imagine in your imaginary world is: Why do we need 50km/h speed limits in towns i don't like speed limits let's just go 150 km/h through them because why not we are definetly not gonna kill anyone, speed limits only exist to make my life harder .