“We think the issue is less that audiences are tired of sequels, and more that there are now so many sequels that they are cannibalizing each other,” Doug Creutz, an analyst at Cowen and Company, wrote in a report on Thursday.

Nor is it just that the summer offerings were particularly awful. “The data suggests differently,” Mr. Cruetz wrote, noting that the summer’s 29 widely released movies had an average score of 57.7 percent positive on the review-aggregation site Rotten Tomatoes, the highest in 16 years.

The lack of clear answers has led to hand-wringing — “Could This Be the Year Movies Stopped Mattering?” asked a Wired headline last month — and studio theorizing about impossible-to-prove factors, like a decline in patrons who decide what film to see while standing in line.

Most people would never consider arriving at a theater without a specific movie in mind. Astoundingly, though, more than a quarter of all ticket buyers still decide what film to see only after showing up, according to PostTrak, an audience polling service owned by comScore. Theaters offer supporting anecdotal evidence. “Our members say the most common questions their ticket sellers get are ‘What’s good?’ and ‘What’s playing next?’” said Patrick Corcoran, vice president of the National Association of Theater Owners.

Still, while data is scarce, PostTrak does show an erosion. In summer 2014, about 32 percent of people made their decision while in line at a theater. In 2015, the number was about 28 percent. PostTrak discontinued research on this audience segment in March, leaving studios to guess at what happened over the 2016 summer season, which started on May 6 and ends on Monday.

If the just-show-up crowd is dwindling, the reasons include the comparative ease of other forms of entertainment (HBO Go, Netflix); the increasing cost of moviegoing (now $17.25 per adult at the ArcLight chain’s Hollywood location, before 3-D upcharges); and the movie business itself, which has aggressively pushed one kind of event movie (lumbering, visual-effects-driven sequels) at the expense of variety.