I suspect a little bit of wool pulling here. When I was on the run we used to rig on route, yes getting your boots and leggings on whilst going round corners was an art. The driver always used to rig when he got to the incident. A lot of the drivers kept their boots and leggings in the pump bay so they could start pumping and then get rigged. However if we had a shout in the middle of drill (remember that?) the driver just jumped in and off we went, no delay for the driver to get his boots off.
When the policy changed so that the crew got rigged before the appliance left, I guess tthe driver issue came to the surface and the reason is an excuse to hold onto the old habits.
Officer to driver "why aren't you wearing your boots?", quick thinking driver " I can't drive safety with the boots on Guv"