While we can’t speak on behalf of Daniels’ treatment off-screen, it seems clear that the character C-3PO’s sidelining has a lot to do with audiences’ unconscious bias against non-human characters. When it comes to characters who aren’t treated as human by the narrative, audiences may come to love them, but they also tend to forget them quickly. There are the “real” characters (Luke, Leia, Han, Obi-Wan Kenobi) and then there are the bonus characters like R2-D2 and C-3PO. The fact that those robots have more screen time in the first movie than Kenobi doesn’t change this perception.
It’s not just robots affected by this bias, as made clear by the popular observation (first on Tumblr, then everywhere) that it kind of feels like the Scooby gang is missing a member. “Every time I look at the mystery gang I have this visceral feeling that someone is missing. But nobody ever is. Who are they? What happened to them?” goes the original post that started this debate. “Something deep within my lizard brain is telling me there’s a sixth member that has been, for unknown reasons, banished from this timeline and our collective memory as a species.”
The answer, many speculate, is that we instinctively don’t see Scooby as a full person. We look at the picture of Mystery Inc. and conclude we’re looking at four people and their dog, not five individuals. The fact that our brain knows it’s five characters but our gut thinks it’s four may be what creates the feeling that someone’s missing here. If they did add a sixth member, and Mystery Inc. became widely known as a six-person group, there’d probably still be posts out there about how it feels like there’s a secret seventh character we’re all forgetting about.