It's because Marvel's plate when it comes to films is full but Daredevil can be done on a TV budget.
Ant-Man and Doctor Strange are both going to be film franchises and there's also been talk of Captain Marvel, Black Panther and Inhumans. That's going to cause Marvel to have to step up their production and release schedule for Phase 3 by releasing 3 films a year and/or extending Phase 3 by another year. (Personally, I feel like BP and Inhumans can wait for Phase 4.) That plus a Ghost Rider reboot will need a massive budget to pull off correctly. Now if Sony decides to sell the Spider-Man rights since the last three films have been less than well-received critically or if Fox's Fantastic Four reverts because the film is a massive bomb, then that'll put Marvel Studios in the position of making four films a year. That's a full slate for any studio and I can't see Marvel pumping out more without hurting the brand by oversaturation.
Other properties like the announced Netflix series along with other properties like Blade, Moon Knight, Punisher, Runaways, She-Hulk, Black Widow, Hawkeye and Winter Soldier can be done on a TV show's budget. When the most expensive costuming choices of any of these involves green body paint, that's an obvious choice for television instead of a full feature film since the marketing budget would be too high to compensate for the lack of special effects.
Keep in mind when looking at what's likely going to be Phase 3
2015 Ant-Man
2016 Captain America 3, Doctor Strange
2017 Thor 3, Guardians/Hulk Crossover
2018 Captain Marvel, Avengers 3
It's obvious to say that Marvel has it's hands full right now. Then when you consider that Phase 4 is going to involve a fourth Iron Man film alongside Black Panther and the Inhumans with three films a year + competition from DC + Fox's films + an animated Power Pack film if Big Hero Six works, there will usually be a superhero film in theaters at all times and no room for street level heroes.
Keep in mind that everyone I listed aside from Punisher and the Runaways has been an Avenger and Marvel Studios has stated that if the Netflix series are successful, we could see them on the big screen, it's safe to say that most of these characters will be joining the Avengers except for Black Widow and Hawkeye who are already members of the team.
Even aside from oversaturation and budget reasons, Marvel wants to introduce properties to other mediums. They're involved in Publishing and film, but branching into other mediums is how the brand stays fresh. Agents of SHIELD is cool but they have to poach villains from other heroes or invent their own. Agent Carter on the other hand can introduce a Previous Madame Hydra before Viper takes on the role as well as Heinrich Zemo as the father to Helmut along with Nick Fury Sr. but a prequel series has next to no crossover potential and is even more limited by what characters it can use.
Bringing A and B-list heroes to TV allows for more interesting villains along with more crossover potential. So if you can do a character cheap, find a way to have Scarlett Johannsson and Robert Downey Jr cameo in Phase 3, branch into another medium, save on marketing, expand the roster of the Avengers and introduce enough villains for a potential Thunderbolts film, then why shouldn't Marvel do Daredevil on TV?
should have been an Avenger a long time ago.
