Hollywood has many more ideas for movies then they have time to make them, which is why many ideas sit in development hell for years. Sometimes, however, ideas are ready to release and sit on a shelf anyway. Often this happens because somebody along the way realizes the movie isn't very good, and so they wait for the right time to dump it, and try to make some portion of the investment back at a time when it will do the least damage.
Sometimes, however, the movie is actually pretty good and the reason that the movie sat around is ridiculous. Here are a few times that good movies sat around with nobody to watch them.
Cabin in the Woods
How Long it Was Delayed: 2 years
Why? Cabin in the Woods is one of the more recent, and popular, examples of a movie that sat on a shelf ignored. Chris Hemsworth was mostly unknown when he made it, but by the time the movie was released, he was Thor. The main reason that this one sat around is that MGM, who originally owned the film, went through a change of leadership, after very nearly going bankrupt, and the new bosses just didn't want anything to do with movies that the old bosses had been responsible for. Thus, this one sat around until MGM could offload it to a different studio, which took some time.
Henry: Portrait of a Serial Killer
How Long it Was Delayed: 4 years
Why? When the MPAA got their first look at Henry: Portrait of a Serial Killer they gave it an X rating. This was 1986, before X was replaced by NC-17. As such, there was no way the film was going to get any sort of serious release, as X ratings were usually associated with actual pornography. What's more, and this is when it gets weird, the MPAA apparently told the studio and director John McNaughton that there was literally no way to edit the film down to an R-rating. This meant the movie sat unreleased until the new NC-17 rating began in 1990, so that the movie didn't have the stigma of the X.
How Long it Was Delayed: 1 year
Why? Fanboys is a fun little movie about a group of friends who go on a road trip to steal a rough cut of Star Wars: The Phantom Menace. However, if you saw the initial release of the film, then there's no real motivation for the characters to want to do this. This is because the initial driving force behind the plot is that one of the characters is dying of cancer. Initially, it was felt that the cancer storyline would be too depressing for the audience. This meant that the film was reshot and edited in order to cut out any mention of the c-word, which delayed a perfectly good version of the movie from being released. You can now find the original version on DVD.
Take Me Home Tonight
How Long it Was Delayed: 4 years
Why? Take Me Home Tonight is a fun comedy about the 1980s that was released in 2011 that had been made in the previous decade. The reason for the four-year delay comes down to one thing: drugs, specifically cocaine. Topher Grace wrote the movie as well as starring in it and as such the film was close to his heart. He stood firm on the belief that all the film's drug use was important to the soul of the movie, and so he would not let it be taken out by the studio, who didn't know how to market a cocaine-sniffing teen comedy. The fight lasted until a new production company bought the film from Universal, and let it out as it was.
How Long it Was Delayed: 6 years
Why? This one is a film that you likely haven't heard of, in large part because the movie took six years to ever be seen. The major issue was one of editing. The writer/director, Kenneth Lonergan, was supposed to take his three-hour movie and cut it down to 150 minutes. It became so difficult for him to do that he ended up borrowing money to pay for the editing. Three years after the movie was finished he got the film down to the required length, but couldn't pay the money back. Then the lawsuits began, which of course delayed things further. Several others took different shots at editing the film, including Martin Scorsese. The few who have seen it have generally thought it actually turned out well.