Why Air-Cooled?
So, an air-cooled engine has no need for a radiator, a water pump, coolant, hoses or any other associated parts a liquid-cooled engine has.
An air-cooled engine doesn't have coolant leakage problems and won't ever require things like the water pump or radiator to be replaced, which can be a great thing. Typically, they're lighter than liquid-cooled engines, too, because they have fewer parts.
Air-cooled engines also warm up a lot faster than liquid-cooled engines and don't have any risk of the coolant freezing, which is beneficial if you're operating the vehicle in extremely cold temperatures.