How is a split drop any less safe than a a shore dive? Especially if you have a surface swim. If you had a 15 min surface swim out, you have more than a 15 min surface swim in to shore towing a casualty. How many shore divers have the emergency gear (AED, O2, etc.) that is available on a boat. Once you are on shore, you can call for help, but it will take a while to get there, even if you are near civilization.
People routinely dive without surface support. Why should it be mandated for boat dives? If you want it, you can pay extra for it. Otherwise, accept it the way you accept all the other risks of the dives you choose to do.
Having a heart attack 30 min from your boat is safer than having a heart attack 30 min back in a cave. At least you have access to the surface while waiting for the boat.