For us it was two reasons.
1. Math. After looking at our F350 and our Raptor Toy Hauler I realized I needed a dually to be in a better towing capacity. But no way could I use a dually for a daily driver. Plus I didn't like having that much weight in charge of my truck, got into one scenario where I had to brake hard and fast so I didn't hit the car in front of me. I didn't like that one bit
2. Bathroom on wheels. I love my wife, but I knew every rest stop along our route, with the Motorhome I can fly by those rest stops and she remains happy.