Because it's less expensive, the car is nicer to drive, and in the past trucks weren't as ubiquitous as say Bonaire. Safe?? really?? now you're just arguing...if you want a truck get one, just saying I've dived many of the "dirt road" sites in the past from a car and it wasn't a big deal. Admittedly post-covid might now be a factor.
In my 13 trips to Curacao, I rented a "car" only once for a couple of days only to return and get a a truck in its place. Never went back to a car at all nor had any problems finding a truck or be more expensive at all. And yes, it is safer with the equipment separated from the passenger cabin especially when you hit the breaks when you a pothole at the last minute with all of the tanks, weights and other heavy equipment behind you.