Loki has become an iconic villain in the Marvel Cinematic Universe, so much so that his popularity has eclipsed some of the heroes in recent Marvel movies. Despite this, Kevin Feige and Joss Whedon decided to cut him from Avengers: Age of Ultron. In an interview with Digital Spy released earlier today, Tom Hiddleston explains why he was cut from the movie in the clip below.
So there you have it, the fact that we love and respect Loki is the reason why he was cut. Subconsciously, viewers assigned him as the main villain who must be orchestrating dastardly plans. In order to keep the movie about Ultron, and not about Loki, directors had to cut his role out entirely. While Loki's original appearance in this film was intended to be short, his popularity should prove his continued demand in new Marvel movies. There is still speculation about whether Loki will appear in Thor: Ragnarok, which is scheduled to be released in late 2017.