Lets start with the number one reason, cost . If you search around for todays 4x4 atvs and rtvs (such as mules, rhinos, rangers, prowlers) prices all start at about $6500 or some of them twice that.  I guess you could spend more and get less if you want. For that money you get a bare vehicle, no cab, no heat, no radio, no comfort, not even a windshield to keep the bugs out of your teeth!  By the time you put a cab and heater in your rtv you've got between 10-15,000 dollars in it. For that kind of money you and two of your buddys could be roaming the county side each in your own mini truck.  You are going in saving thousands and your getting a great 4x4 off road truck that can do anything an atv can do and haul more than any rtv.