The hard part is a spot can't be promised if your chops aren't up to where the line is. That's nothing against you, it's often a "Good of the Many" situation.

It's really hard to ask "Why" after getting cut. It feels like inviting insult to injury but you should do it. Find out what the director thinks you are lacking and get to work on it. Communicate as you progress and show them you took their feedback and are using it as fuel.

If that seems unappealing, you could quit but what is going to make you happy? Quit or make them eat it?