Could the reason simply be because they haven’t been very good?

Early summer movies underperform at box office
LOS ANGELES (Reuters) – Moviegoers are not following the script written for them by the Hollywood studios. In a sign that big-budget sequels may be losing their allure, North American ticket sales for the first three big films of the lucrative summer season have not kept pace with their respective predecessors.
The numbers for “Spider-Man 3,” “Shrek the Third” and “Pirates of the Caribbean: At World’s End” are still impressive, and the studios do not seem too worried. For the most part, they blamed increased competition, although — apart from the big three — there is little else of significance playing in theaters.
The third film in Walt Disney Co.’s “Pirates” trilogy led the Memorial Day holiday weekend with four-day sales of $156 million, setting a record for the busy period, the studio said on Monday. The previous record of $123 million was set last year by “X-Men: The Last Stand.”
The Friday-to-Monday haul for “Pirates” was boosted by estimated sales of $14 million from Thursday-night previews, drawing moviegoers who likely would have seen the film at some other time during the weekend. Disney’s inclusion of the Thursday tally raised eyebrows at other studios.
If the Monday and Thursday figures are stripped out, the traditional three-day sum of $115 million pales against the then-record $135.6 million start of last year’s “Pirates” installment, “Dead Man’s Chest,” as well as those of “Spider-Man 3” ($151 million) and Shrek the Third ($122 million).
Mark Zoradi, president of Walt Disney Studios Motion Picture Marketing and Distribution, said he was “as pleased as could be” about the opening, given the tough competition.
On a worldwide basis, the film has earned $401 million, with hefty contributions from the likes of Britain ($26 million), Korea ($18 million) and Germany ($16.8 million).
The first film, 2003’s “The Curse of the Black Pearl,” finished with $653 million worldwide, while “Dead Man’s Chest” topped out at $1.1 billion.
Meanwhile, the previous weekend’s champion, “Shrek the Third” has earned $219 million in North America after 11 days. By contrast, “Shrek 2,” released at the same time in 2004, had earned $260 million through the Memorial Day holiday. (The earlier film opened two days earlier, however.)
The latest installment in DreamWorks Animation SKG Inc’s family comedy series earned $69.1 million during the four-day weekend, the studio said. But the three-day portion of $53 million represented a hefty 56 percent slide from its first weekend.
Anne Globe, head of marketing at DreamWorks Animation, said she was “very happy” with the new film’s performance, and comparisons with “Shrek 2” were invalid because of the tougher competition.
Sony Corp’s “Spider-Man 3” was third for the weekend with four-day sales of $18 million, driving its total to $307.6 million. “Spider-Man 2,” also released in 2004, had earned about $328 million in that time.
“It’s really hard to complain about $307 million,” said Rory Bruer, president of domestic theatrical distribution at Sony’s Columbia Pictures unit. “Ultimately, we’re going to be fine.”
According to industry analyst, “Spider-Man 3” took 24 days to hit $300 million, two days slower than 2004’s “Spider-Man 2” and five days slower than 2002’s “Spider-Man.”
But on a worldwide basis, the new film is on track to beat the $821 million total of “Spider-Man” later this week, said Columbia. “Spider-Man 2,” despite a stronger start, finished with $784 million worldwide.