Yes, but by that time you're driving the truck around neighborhood streets, getting up to 25 mph at most before you stop at the next stop sign. Not nearly as much force being applied as making turns at 55 mph. During the long drive from the warehouse to that city (and the specific neighborhood), the boxes are packed in tightly.

Plus, I seem to recall that they also optimize by giving the driver a route to follow and planning the boxes to be packed in order, so that only one row is being emptied at a time. I know my UPS driver friend has told me UPS does this, and it's an obvious optimization so I'm sure Amazon does it too.