They'd be wrong. These shows are alive and well and living in cyberspace, and they're not being produced by Hollywood studios, but by their devoted fans.
Fans creating their own stories using the characters from TV shows probably is as old as TV itself.
In the 1980s, fan fiction got a huge boost, thanks to desktop publishing and the corner copy shop. First off, they're actual seasons, with a series of shows that continue the drama from the TV episodes. Fanfic is often wild flights of the writer's fancy. Virtual seasons attempt to stick close to the original content and are presented as if they are actual episodes of the programs. Many of them are written in teleplay style and are surprisingly well written, with all of the stage directions and scene descriptions so you can visualize the show as if you were watching it on television.