Why them and not you?
Essentially the director and / or writer knew them, trusted them and they are right for the role. Simple.
So how do you get to that place?
You have to gain the trust of the casting director.
Which is fine for me to say but if you aren’t getting in the room how can you do that?
It’s NOT all about your acting. In fact your acting is a tiny part of what you need to do in the casting process. Getting in the room is more about being the right person, not the best actor. But to be seen as the right person you have to have all your tools working for you.
You have to know your niche and type and only submit on those roles
Over submitting by you or your agent tends to make you invisible – which is why having multiple agents is rarely a good idea.
You have to tailor your material to your type
So when you are submitted you look right. The casting director doesn’t have time to look at every resume or reel. In fact they look at very few. They look at your head shot and that tells them whether to look further or not. If you don’t look right for the role it’s all over right there – unless they know you and trust you can do the job.
If your head shot looks right but your resume and reel don’t reflect the role – both in ability required and type then you won’t get an audition.
If you have the right material and submit on the right roles the casting director will trust that you and your agent know what you are doing and are more likely to take a chance on you.
And then you are in the room.
The purpose of any audition is not all about getting THAT role.
It is to gain the casting directors trust so that they remember you and ask to see you again and again and again.
Then you are the actor booking all the auditions.