Netflix is the perfect medium for Dardevil, Iron Fist, and Luke Cage. The 3 major reasons are, on Netflix you don't have to worry about the FCC and ratings, you can tell a complete story in a 13-16 episode arc, and Street level heroes are too different from the Heroes in the Marvel Comic Universe films.
The biggest reason they still haven't made a Deadpool movie that is always given is "We can't get a PG-13 Rating" and superhero movies are traditionally viewed as family fair. This is in my opinion why the best comic book arcs for your street level heroes either didn't get into the movies or got in in a bad way. They had to clean up comic book characters that simply wouldn't work for a family audience. Look at some story arcs from Daredevil, his first love is murdered gruesomely, his 2nd love becomes a heroin addict and a porn star and sells his secret for smack, and racism, gang violence, drug use, and other brutal crimes are day to day on the streets of new york including prostitution and pornography. You can't capture the essence of the dark and gritty world of Daredevil unless you're Christopher Nolan and you're worried about a PG-13 rating. On Netflix you don't have to worry about a rating or about appealing to a mass audience. The viewership doesn't have to be as high.
In a film you're given 2 hours to tell a complete story, and if you get a trilogy maybe 6-8 hours to tell a complete story, knowing that you have to tell 3 complete stories in every film. In a traditional TV show you need to tell 24 complete hour long stories and within that tell 24 hours of story. On Netflix, knowing that you will watch every single episode likely in one or 2 sessions. You don't need as inclusive 1 hour stories, and you don't need the little stand alones. Think of this from the point of view of the Immortal Iron Fist, he has to fight in the Tournament of the 7 cities, you don't need every fight in every episode. You can advance the entire story in each episode but you can have a fight per episode. Or give a flashback from a previous Iron Fist in every episode, but stick to the overarching plot. Daredevil can have a different case in every episode, but the main story and how that case fits in can be continued without having to explain every episode. Game of Thrones and the Walking Dead would be better shows and are more fun to watch in one sitting.
In the Marvel Comic Universe now there is one universal threat "HYDRA" they are now the MCU's biggest bad guy and this villain will exist in every single film from now on. HYDRA could get your family or friends if you are a normal person. But in the MCU all of the Avengers are impervious to this and that's why none of them have secret identities. Secret identities can't exist in the larger scheme of the universe because they all worked for and were assembled by HYDRA agents and Shield. Is Peter Parker existed in the MCU he was outed at the end of CA-TWS and Aunt May just got shot and her head was plopped on the top of the Empire State Building and Mary Jane would be next. Also, HYDRA would have known all along. Tony Stark has no secret identity, neither does Rogers, or Thor. Falcon does but remember they made sure that he's not a shield agent so his secret is safe and so are his loved one. Now Daredevil has no family but he usually has friends, and a girl. Iron Fist has no family but he has students at his Dojo, Luke Cage in the comics is a family man with a superhero wife and kid. He's got people that love him. This is why they have to keep their secret a secret and also need to be a secret from Shield and Hydra so they can't appear in the movies or be Avengers.
Final thought for why they are perfect, they can all be shot in the same locations. You can have tie ins, Murdoch defends Luke Cage for being a mercenary, Misty Knight cameo's in both Daredevil and Iron Fist, Murdoch trains at Iron Fist's dojo. Rand Corp is seen in all 4 shows. Jessica Jones can be a villain in 1 episode of Daredevil and obviously is Luke Cages wife.