Perhaps it can be chalked up to the wartime shortages - all the good actors were fighting WWII, as were all the good directors, screenwriters, set builders, sound recorders, etc. They started with a bad story containing far too many contrivances, requiring the first ten minutes to be non-stop exposition which then had to be repeated a few times throughout the film to make sure we all understood. Then they brought in the uninspiring leading man, and the blocky staging by the director, and put them on a minimal set (a train's dining car and sleeping car). Add a few shuffling black porters and some classic wartime German stereotypes, and not a lot of imagination, and the result is this time-filler.
