Why did Disney go with Netflix to air their Marvel's Defenders' series?

Because Netflix is better suited for the type of show that Daredevil, Jessica Jones, Luke Cage, and Iron fist want to be. More adult than would fly on broadcast channels like ABC, and not suited for Disney's branded channels (cartoon and teen programming). And Netflix offered substantial benefits that the traditional broadcast model did not Straight from the horses mouth:

Produced by Marvel Television in association with ABC Television Studios, this groundbreaking deal is Marvel’s most ambitious foray yet into live-action TV storytelling.

"This deal is unparalleled in its scope and size, and reinforces our commitment to deliver Marvel's brand, content and characters across all platforms of storytelling. Netflix offers an incredible platform for the kind of rich storytelling that is Marvel’s specialty," said Alan Fine, President of Marvel Entertainment. "This serialized epic expands the narrative possibilities of on-demand television and gives fans the flexibility to immerse themselves how and when they want in what's sure to be a thrilling and engaging adventure."

They also felt that the story of the week format would fall short for the Defenders series. The binge watching (on-demand) factor makes the shows more like Avengers movies, than a typical tv show. Netflix's proven history of original content, a first for a non-traditional video service, help boost that.

"Marvel’s movies, such as 'Iron Man' and 'Marvel’s The Avengers,' are huge favorites on our service around the world. Like Disney, Marvel is a known and loved brand that travels," said Netflix Chief Content Officer Ted Sarandos. "With 'House of Cards' and our other original series, we have pioneered new approaches to storytelling and to global distribution and we're thrilled to be working with Disney and Marvel to take our brand of television to new levels with a creative project of this magnitude."

Additionally, the size of the seasons wouldn't fit typical US show standards. A typical US series requires about 26 episodes (less if canceled). Netflix was willing to do mini-series of 13. You could argue that ABC could show a 13 episode series, but the normal audience of ABC would not appreciate it. Netflix was also willing to do it blind.

There was nothing small, however, about the size of Marvel’s pitch: It wanted an upfront order of all five series, without pilot episodes. That approach seemed to rule out broadcast networks like ABC, which, like Marvel, is owned by Walt Disney, and which carries other Marvel series, like the espionage adventure “Agents of S.H.I.E.L.D.” (After a widely watched debut in the fall of 2013, “S.H.I.E.L.D.” has cooled off in its second season, drawing about 4 million to 5 million live viewers an episode.)

Netflix, the streaming video service, had started its political thriller “House of Cards” with a two-season guarantee, and was willing to make an even bigger commitment to the “Defenders” project.

Ted Sarandos, Netflix’s chief content officer, said of striking the deal with Marvel, “We were taking what I thought was a pretty measured bet on someone with a great track record of serving a very discriminating fan base.” Although his initiation into the series was somewhat rapid, Mr. DeKnight said the Netflix model allowed “Daredevil” to spend an entire season gradually unpacking the origins of its characters.

“When you’re working on a network show, especially a pilot, the notes you get are, basically, ‘Cram the entire first season into that first episode, so everybody knows what they’re going to get,’ ” he said. On Netflix, Mr. DeKnight said: “It really is the exact opposite. It’s more, ‘Slow things down, let it breathe, explore it.’ ”

Again, the binge-watch factor helps. Netflix doesn't think their audience has ADHD. No stupid recaps at every episode start, no rewind at every commercial break. Those minutes add up.

The Netflix model also means that subsequent episodes don’t have to spend time recapitulating what happened in previous installments. “We had a brief discussion about it,” he said, “and decided: ‘Eh, why does that matter? People are going to binge-watch this.’ ”

Money. And a suitable station.

It's not like any of the MCU Netflix shows is suitable for airing on the kid-friendly Disney channel, or broadcast on ABC. Similarly the other Disney-owned networks of A&E, Lifetime, and ESPN are not good matches for the material.

Unlike most major studios, there is no associated subscription premium channel associated with Disney. Warner Bros. has HBO, Fox has EPIX, and MGM/UA has Showtime, but Disney never got their own premium subscription channel. And premium subscription channels is where the more extreme, short-run shows thrive. Not having to answer to censors or sponsors makes it easier than using broadcast means.

Disney films used to premiere on premium cable on the STARZ network, but Netflix outbid STARZ for first-run Disney/Pixar films. HBO used to be the richest network around. Since 2013, Netflix has been doing bigger revenue than HBO. The budget for the first season of The Crown was around $130 million. The cost of season six of Game of Thrones was $100 million. Just saying.

Netflix is where the money is these days.