The number of people who actually do that is miniscule.
Ford Ranger Super Duty wasn’t even available with a factory tub at launch, and the Toyota Landcruiser 79 doesn’t have one at all.
I get it - it would be amazing from maintenance and economy perspective, especially on fleets. But for private owners and campervan hirers it makes little sense. Even something like V2L on most EVs suck for even weekend camping, let alone a whole week.
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.