I've done this research in 4 different large metropolitan areas, including Chicago.

There are a handful a major problems:

1. They don't guarantee a specific make, model, or configuration. They guarantee a hitch receiver, but they don't guarantee minimum payload capacity, brake controllers, tow mirrors, axle ratio (important for towing), or engine configuration (also critical for towing). This alone is pretty much a breaker. Again, a truck isn't any use if it cannot legally tow your configuration.

1b. Rental trucks are almost always lowest trim levels. They're not going to have a tonneau cover, advanced safety features, or creature comforts of the truck you own/lease.

1c. They do not guarantee fuel capacities or offer extended range tanks. This can be a major problem when you're towing in the middle of nowhere or in mountainous areas.

2. They do not guarantee they will have inventory available when you need it. Everyone wants to go camping and move during major holiday weekends, so it's neigh impossible to actually rent one during peak times. This argument holds against any sort of "just rent from a niche provider". Renting doesn't work if somebody else is renting the vehicle you need during the time you need it.

3. It's wildly inconvenient to actually rent a truck. For example, Enterprise does offer truck rentals - but they come from truck-centric rental locations, geared towards business and commercial use. They basically only operate during standard business hours. That means getting a rental truck requires taking time off.

Some companies offer fleet rentals that basically solve all of the issues above - except these are really more like leasing programs. You can get a month-to-month rental, but prices are pretty absurd. Not to mention, you still have a truck sitting in your driveway for the part of the month you're not traveling.

All good points, thank you for expanding.