There's also the question of whether or not people need rescuing. Simply because you see somebody adrift, even if they're waving their arms, doesn't mean it's necessarily a true emergency. And now we would make container ships stop and investigate? That doesn't work.
Still, even if the data was simply collected and logged, perhaps others could sift through it for clues about where rescues might need to take place. With the cost of cameras and bandwidth continuing to go down, it wouldn't be a crazy expensive thing to install.
