IIRC, the dive bus doesn't allow solo diving, that plus they determine where you are going to dive, it isn't really your choice. Some people like having their itineraries determined for them, some don't. If you go to Curacao and don't take the Dive Charter Curacao RIB to the East end of the island, you're really missing out on the most spectacular/ least trampled / least loved-to-death reefs (hint you need a car to get to their dock)
A car is really a necessity on Curacao if you want to see the island and as noted earlier, the car rental companies don't seem to care if you use a car to transport your "stuff", so why pay extra?