How is the twilight zone associated with mystery?

Twilight Zone was an anthology show- a format common in Radio drama ( such as suspense, even Dragnet to some extent ( but Dragnet had repeating police characters) Each tale was complete in itself, there were no repeating or regular characters- anything could and did happen. Happy endings, or even non-violent conclusions, were few and far between. All of the basic occult, weird and science-fiction plot ideas were used including time travel, usually accidental- a Pawnbroker ( of all people) is taken back to the role of Hitler at the close of the War in the Bunker, for example) There was little comedy- but some comic relief... For some reason while suspense and unpredictable plot elements were- on course, they avoided Titanic waters!