Because you want to install equipment such as air compressors, pumps, welders, cranes or water tanks, or you want to carry bulky items like ladders, and/or you need accessible and ergonomic lockers, drawers etc to store your tools and equipment without having to dig around the tub.
Because you want to install equipment such as air compressors, pumps, welders, cranes or water tanks, or you want to carry bulky items like ladders, and/or you need accessible and ergonomic lockers, drawers etc to store your tools and equipment without having to dig around the tub.
Same reasons as you’d do this on an ICE truck.