Press releases from show producers, publicity stunts by cast members and simple reportage are a few of the ways that members of the press find out about spoilers for television shows. In fact, many “leaked” spoilers are planned to whip up interest in a show or to increase market share.
Timely leaks and other spoilers usually have to do with television advertising revenues. For example, soap operas are so named because soap manufacturers were commercial sponsors of early radio versions. Because these advertisers invested so much money in air-time during the shows, they also had say about plot lines, marketing gimmicks for the shows, etc.
The same is still true today. Also, show and network producers compete to increase ad revenues by convincing new advertisers to buy time during their shows. Often producers “leak” plot details and plan cast members publicity stunts to keep private business promises they’ve made to advertisers. It’s common that big leaks and big stunts are part of a much larger marketing plans to introduce advertisers’ new products and services leading up to awards shows like the Emmys and the Oscars. To that end, many press releases about specific shows reveal big plot twists but require that media outlets not release the information before certain dates.
Occasionally reportage by a reporter who covers the entertainment beat uncovers a real surprise. However, real scoops are rare.