People in garbage trucks don’t experience the same magnitude of force in a crash of equal speed, even without crumple zones, for a few reasons:

• Sheer mass of the garbage truck means that the same amount of momentum transfer results in less force to the humans inside. A garbage truck might weigh literally 20 times as much as a kei truck, which means that an abrupt collision will transfer 1/20 as much impulse to the passengers (as most of the force goes into changing the speed of the truck). Even collisions with still objects (trees, walls, poles) result in less force on the passengers, as a lot of the energy ends up deforming or disintegrating that stationary object as a crumple zone.
• Driver/passenger height in a garbage truck is generally above where the collision/deformation occurs. The passenger compartment isn’t under as much crushing force in a garbage truck crash compared to a kei truck at normal human height.
• The height of a garbage truck gives a lot more physical structure to dissipate the forces in a crash.

So the exact same shape/proportions of vehicle can be vastly different safety when large versus small.