LOS ANGELES — American moviegoers sent a clear message to Hollywood over the summer: We are tired of more of the same.

But don’t entirely blame the sequels and superheroes.

The film industry had its worst summer in North America, still the world’s No. 1 movie market, since at least 1997, after adjusting for inflation. Between the first weekend in May through the end of August, ticket sales in the United States and Canada are expected to total roughly $3.9 billion, a 15 percent decline from the same stretch last year, according to Rentrak, a box office data company.

Analysts in the spring had predicted an 11 percent drop, citing viewing distractions like the World Cup and scuttled release plans for films like “Fast and Furious 6” and Pixar’s “Good Dinosaur,” which both had production problems. But the decline was worse than expected, and the reason, analysts and studio executives said, may have been a nasty case of déjà vu.

Tom Cruise’s futuristic “Edge of Tomorrow,” for instance, looked like a hit — and that was exactly its problem. The title was too similar to “The Day After Tomorrow,” released in summer 2004. The barren landscape too closely resembled Mr. Cruise’s 2013 film “Oblivion.” Characters walking around in robot exoskeletons? Been there (“Pacific Rim”), done that (“Real Steel”).