Submarines may fire torpedoes from several thousand yards away, and get strikes.
But in most cases the target doesn't know there is a torpedo coming their way until it close enough to be spotted by a lookout.
But B-17s are not the stealthiest aircraft out there, someone's going to spot it and maybe the splash of the torpedo too.
There's a lot of run time on a maybe 40 mph torpedo, and a lot of time for even a slow supply ship to maneuver .
I think a lot of us has seen photos of the wild maneuvering wakes the Japanese fleet made during the Battle of Midway, when B-17s dropped bombs from high altitude , not a single hit.
No matter what kind of target computer, or bombsight you've got, they can't work if the target has a random maneuvering pattern.