As summer began last year, the movie-release schedule was a parody of itself: What on first glance seemed the usual raft of sequels became, on further examination, a less-usual raft of threequels, beginning with the latest iterations of “Pirates of the Caribbean,” “Shrek” and “Spiderman” (all released in May), but also including “The Bourne Ultimatum,” “Ocean’s 13” and “Rush Hour 3”; the fourth or fifth “Harry Potter”; and the fourth “Die Hard.”

It’s easy to make fun of the movie industry for such pathetic, “The Player”-like lack of ideas. But of course it’s the audience that dictates what gets released and, as can be seen from the annual box office returns, the top seven slots include no less than five threequels.

There are a lot of great movies that get released, so this isn’t an aesthetic issue. But at a certain point someone is going to notice that the industry is in effect cannibalizing itself. This point doesn’t get noted enough in analyses of the film industry. The Times’ year-end wrap up goes out of its way to note that the three top grossing threequels didn’t do as well as their respective predecessors, if you take inflation into account. This is good in the sense that too many box-office stories don’t mention the effects of inflation, which obviates most of the silly records bruited about by the industry. That said, the idea that the $300M-plus grosses of the last “Shrek,” “Spidey” and “Pirates” is anything but great news for the studios is silly. (Disney has now grossed more than $2.5 billion from box offices alone from a franchise—based on a Disneyland ride, remember—that was considered a joke before the first film was released.)

But of course, while box office was up four percent this year, attendance was about the same as last year’s. Which means that the many threequels had to find their audience from people who were giving up seeing other movies.

Again, I don’t think this hurts smaller, presumably better, films; no one went to see “Pirates” instead of “No Country for Old Men.” And the trend does have to end at some point, or the movie industry will devolve, in about the year 2019, into a slate of six or seven films, total, annually, ranging from “Mission: Impossible: 9” to “When Wolverine met the Invisible Woman,” the long awaited X-Men-meet-the-Fantastic-4 epic. But it does take the movie industry a step or two further down a dead-end street.