You can travel at car speed limits. This comes into play in several of the western states, where you must use truck speed limits when towing a trailer. In California it is 55.
Just pull over and turn around to make lunch.
One rig to back up and park. Easier to park.
More folks can ride in comfort in a motorhome.
Disadvantages: Costly to purchase, insure, operate. Costs just as much sitting in your driveway.
Unless you drag a "toad", not too convenient for exploring from an established location. you have to put everything away, pull up the outriggers, pack for travel just to go on a day adventure.
Pulling the "toad", you cannot back up any appreciable distance before it jacknifes. If you drive into a situation that you can't just wheel around in, you have to get out, disconnect the toad, turn the motor home and reconnect.
Advantages of the 5th wheel/truck:
You don't pay to insure the 5th wheel for liability. You can choose other coverages, but the tow vehicle's insurance is what applies to both when in motion.
The pickup has other utility as a second car, to haul other things, etc. The MH, not so much.
You can back up and turn around anywhere you are proficient to do so.
Once you set the trailer up in a site you are good to go exploring, shopping etc with the truck.
Disadvantages of the 5th wheel/truck combo:
It takes some proficiency to feel comfortable and enjoy traveling with one. MH's are pretty easy to jump into in comparison.
If you do bring a toad with the motorhome, it is usually an easier, smaller car to go exploring with. The big truck can be a bit cumbersome, especially if you opt for a "fat butt" dually. It is one reason I won't own a trailer big enough to require a dually.