Supergirl is Now Officially DC's Biggest Flop Ever, Theatrical Losses Set to be Over $200 Million - TV Fandom Lounge
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I think it's a mix of reasons, the biggest one obviously being the movie is mediocre. But I think the other big reason is that Supergirl just isn't a franchise most people care about. People would flock to the cinema for Superman, Batman, Wonder Woman, maybe even Aquaman because he's better known. But a story about Superman's sister running around in space? Ehhhh...