It can entirely depend on the deals you get; I was able to rent a Tahoe (largish but not huge SUV) and drive it across the country and back for about a grand; unlimited miles; and I've done similar with a minivan. You get a brand new vehicle that you can put miles on and it's unlikely to fail you.
True, deals can sometimes be found but that's more work and worry when you should be relaxing on vacation. Combine that with the other drawbacks (dealing with pickup/return, worrying about scratches/damage, not able to have customizations like roof racks, going offroad or through mountains with crap rental tires, etc) and it's easy to see why renting is not more popular.
