The people on the sub know exactly what would happen to them/their families, but it's more than that, it's that the sub is tracked, it's not like the dudes just hit the shore somewhere, unload, and walk it out yknow? That sub is tracked, once it's close to the destination, trust me there's no way the sub's pilots are in a position to just bounce w/ the product (not like tons of coke fit in a suitcase ;P )
And it'll be there (remote controlled) in the future, but for now the tech is just more expensive than the lives. Remember, the guys on the sub aren't dealers/traffickers, they're mules/lower, they get dick for that ride but mx is full of people who'll take that risk for a few $k.