Some of them haven’t been gone long enough to be missed — but all of them are returning.

Reboot mania has spread to the unscripted series arena. Everything from A&E Network’s “Biography” to TLC’s “Trading Spaces” to Food Network’s “Iron Chef” to Discovery’s “Cash Cab” is being revived by hit-hungry networks.

“American Idol” signed off this time last year after a storied 14-year run on Fox. The confetti was barely swept up off the stage before FremantleMedia North America began shopping a revival to Fox’s rivals. NBC is known to be taking a hard look.

“America’s Next Top Model” sashayed off the CW in December 2015, and within six months had relocated to VH1. The show has been renewed for another season, this time with original host Tyra Banks coming back, to boot.

The reason for all the reality TV reruns is the same Marketing 101 factor that drives the endless parade of movie and scripted-TV remakes (not to mention the TV adaptations of movies and movie adaptations of TV series): In an environment with seemingly endless entertainment options, a well-known title stands taller in the crowd. Most prospective viewers already have an idea of what they’re getting, even if the format is inevitably remodeled in some way.

The flood of established unscripted titles also underscores how few new hits have emerged in the reality-competition space. Spike TV has bona fide bragging rights with “Lip Sync Battle,” but that’s about it.

ABC’s success in dusting off the game-show formats “Match Game” and “$100,000 Pyramid” encouraged Fox to recruit Andy Cohen to host a next-generation take on “Love Connection” this summer. “Fear Factor” and “Deal or No Deal” are among the older titles that are poised to be shopped anew.

In this climate, the toughest job in TV is launching a wholly new series format. CBS took a huge swing in January with “Hunted,” in which teams of contestants crisscrossed the U.S. in an effort to avoid a law enforcement-style manhunt. The show struggled to capture viewers and is not likely to be returning on CBS.

The Eye’s next big unscripted bet has a colorful built-in brand borrowed from a different kind of screen: “Candy Crush,” coming this summer.

As popular as they are, remakes and reboots can only go so far. Networks still have to field new players. CBS last week ordered a new series from the “Hunted” team: “Ambulance,” revolving around the life-and-death work of EMTs.

“Things are cyclical in this business,” said Rob Smith, exec VP and head of unscripted for Endemol Shine North America. “Today’s new idea could be tomorrow’s hit format.”