Movie sets gather a lot of stuff: props, costumes, backgrounds, and all the various things used to get a film in the can. After filming is wrapped up, there's quite a bit of time before the movie is released, and who knows whether this one will be a hit or a flop? Storage room costs money, so the leftover props and other items from a film shoot are often discarded. Yes, they may be given away, sold, or recycled, but many iconic items from movies that became classics were just tossed in the trash.
For example, there was only one model of the Death Star from the first Star Wars movie. After filming, it went to storage, but later the storage room was ordered to be cleared out. The employee cleaning it out took the Death Star home. Years later, it was sold to a musician who used it as a trash can! But eventually someone else saw its value. Read about the Death Star and seven other props that were trashed from movies like Gone With The Wind, The Wizard of Oz, and King Kong at Mental Floss.