when you're making a game in 3D, cutscenes all need storyboards and camera angles and stuff and it gets way more complex
in 2D, if say, I have to have a character enter a room, I just spawn them in at the door or something. in 3D, I have to figure out what the best angle to show them entering the door is, and also to make the door open, and also to make it clear to the player that this is the same door that is the room entrance, so make sure to get enough of the room in the shot, etc