on the cutting room floor

Etymology
From the earliest film-editing process, which involved manually removing (cutting) unwanted scenes, leaving the film scraps on the floor of the room used for editing (the cutting room).

Prepositional phrase

 * 1)  Not included in the finalized version of something; deliberately rejected or unintentionally overlooked.
 * The experimental broccoli ice cream flavor was left on the cutting room floor after market research.