The 2013 Emmy Award nominees for outstanding drama series are, from left, “Homeland,” “House of Cards,” “Mad Men,” “Game of Thrones,” “Breaking Bad” and “Downton Abbey” (which is not pictured in this composite image). Showtime, Netflix, AMC, HBO

Nominations for the 2013 Primetime Emmy Awards were announced last week, and while there has been much chatter about Netflix’s history-making “House of Cards” -- the first online-only series to be nominated for a top award -- the list is also notable for what failed to be recognized.

This is the second year in a row that all four major broadcast networks (ABC, NBC, CBS and Fox) were completely shut out of the most prestigious Emmy category, Outstanding Drama Series. Throughout most of Emmy’s 65-year history, broadcast television had a virtual monopoly on TV content creation, and the Emmy Awards reflected that. Then in 2004, something unprecedented happened: HBO’s “The Sopranos” took home the coveted Outstanding Drama Series statuette, the first cable series ever to do so.

For the broadcast networks, it was a precipitous drop from there. In the nine years since, cable series have all but dominated the drama category. The last time a network show was named best drama was seven years ago, when Fox’s “24” earned the award. And it doesn’t look like broadcasters will regain their foothold anytime soon.

So what happened? Critics and analysts attribute the decline of network-TV drama to a variety of factors, not the least of which is the Big Four’s continuing reliance on larger audiences. In terms of viewership, cable programming operates on a more niche-oriented model. AMC’s four-time Emmy-winning “Mad Men,” for instance, attracts about 3 million viewers on a good night. If a network show were to average those kinds of numbers, it would be canceled quicker than one of Don Draper’s extramarital flings. In other words, the Big Four don’t have the luxury of nurturing the kind of sophisticated, specialty programming that can survive on a small-but-loyal following.

“Before cable came along, networks wanted to get a 30 share to be considered successful,” said Robert J. Thompson, a media scholar and director of Syracuse University’s Bleier Center for Television & Popular Culture. “You could never get 30 percent of the entire viewing audience to watch a complicated television show.”

And yet, if there is a divide in the broadcast/cable business models, Thompson pointed to the irony that the two platforms essentially created each other. In the early days of cable, the networks saw their market share dwindle for the first time in television history. With smaller audiences came the freedom to experiment, and that, in turn, paved the way for what is now thought of as the first renaissance of television drama, when shows like NBC’s “Hill Street Blues” and ABC’s “Thirtysomething” added a new level of sophistication to the genre.

“We should remember that the networks invented this stuff,” Thompson said. “They were doing high-quality, serialized scripted drama when HBO was just getting into the series business.”

But the drama renaissance of the 1980s didn’t go unnoticed, and before long, cable networks realized they could not only produce the same kinds of shows, they could do it better. With smaller budgets, shorter seasons and fewer censorship constraints, cable networks found themselves ideally poised to test the waters until they stumbled upon the perfect formula for creating engaging, even addicting serialized TV dramas.

It’s a production model that continues today, with shows like AMC’s “Breaking Bad” and HBO’s “Game of Thrones” created under far fewer constraints than broadcast series like CBS’ “The Good Wife.” The result, some critics say, are TV dramas that are not even in the same weight class, even though they are forced to compete for the same awards.

“I’ve thought for a long time that it’s an unfair comparison,” said Doug Strassler, a critic for the New York Press who covers television, film and theater. “The cable networks have so much more freedom. It’s almost two different genres.”

One big advantage for cable producers, Strassler said, is time. Consider last year’s Emmy winner, the Showtime drama “Homeland,” whose season consisted of 12 episodes. Broadcast offerings are often forced to churn out twice that amount, and that means less time to assess what works and what doesn’t.

“It’s a very short time for hiatus,” Strassler said. “When you’re in the kitchen that long, you have very little time to step outside and see how the food actually tastes.”

More recently, broadcasters have experimented with shorter seasons (“Under the Dome,” a modest hit for CBS this year, clocked in at 13 episodes), but even if networks could solve the problem of time, they would still be left with the problem of censorship. Broadcasters are still regulated by the Federal Communications Commission, prohibiting them from producing the kind of edgier content audiences and critics gravitate toward.

The FCC, for its part, is considering relaxing its indecency rules, and it is accepting public comments on the issue until Aug. 1. Thompson, for one, thinks it’s about time, calling the FCC’s arbitrary community standards “ridiculous.” But he admitted that getting lawmakers to agree to broadcast deregulation is a different matter entirely.

“We know how politically dicey this is,” he said. “It’s the one thing you can get Democrats and Republicans to agree on. They both had a cow when Janet Jackson’s breast popped for half a second at 50 yards.”

With Netflix entering the Emmys race this year and online giants like Amazon getting into the production business, broadcasters are only going find the Outstanding Drama category increasingly more competitive. The question is, should they get out of the drama business altogether? In the end, a production slate full of reality shows and sitcoms may be less prestigious than creating the next “Sopranos,” but if done right, it’s no less profitable.

“I do think networks realize that they’ll never be able to compete again on the prestige level,” Strassler said. “There will be occasional shows like ‘The Good Wife,’ but mostly they’re not going to be quality water-cooler products.”

Still, Thompson said there has been a reluctance -- from all four of the major networks -- to completely give up on serious drama, despite all the signs pointing them in that direction. And it’s not that they haven’t experimented with exit strategies. Thompson cites Jeff Zucker’s now-infamous attempt in 2008 to move Jay Leno to 10 p.m., a time slot typically reserved for police procedurals and hospital dramas. If that scheme had worked, other networks would surely have followed, zapping their 10 p.m. dramas one by one.

“That was a real effort by NBC to simply bow out of that program type,” Thompson said. “Well, we all know what happened to Jay Leno’s prime-time show. It was an absolute disaster.”

The 2013 Emmy nominees for Outstanding Drama Series are “Homeland” (Showtime), “House of Cards” (Netflix), “Mad Men” (AMC), “Game of Thrones” (HBO), “Breaking Bad” (AMC) and “Downton Abbey” (PBS).