Revealing mistake: When Marius is talking to Lestat on the beach, the victim that Lestat drops is a dummy. (00:24:05)
Revealing mistake: Just after the flying scene when Lestat and Jesse land on the rail of the building, when Jesse falls you can tell for a few seconds that she is standing just below the view of the camera because her hand is just sitting there before Lestat grabs it. (00:58:00)
Answer: There are already way too many characters in this movie. Adding the character of Magnus who would only be mentioned in passing was probably just considered too confusing.
Myridon