I think it is safe to say now that these are being cancelled so that they can move to the Disney Streaming Service that releases later this year. While Iron Fist and Luke cage were the 2 least popular Marvel-Netflix shows, Daredevil was the most popular, which means that it's definitely not being cancelled because of the ratings. I think we will see Iron Fist and Luke Cage revived on the Disney streaming service as the two crossover shows, Heroes for Hire (Danny Rand + Luke Cage) and Daughters of the Dragon (Colleen Wing + Misty Knight), as the groundwork for both crossovers has already been laid. Joining them will be Daredevil, as well as Punisher and Jessica Jones after their 2nd and 3rd seasons respectively air on Netflix and they are subsequently cancelled by Netflix. That will give the Disney streaming service 7 Marvel shows, those 5 from Netflix, plus the already announced Scarlett Witch and Loki shows.