Why is Ponyboy finally able to write his English theme?

Ponyboy is finally able to write his English theme after he processes the traumatic events surrounding the death of his friends and the struggles he faces as a Greaser. His experiences inspire him to express his feelings and thoughts through writing, allowing him to connect with his emotions and share his story. Ultimately, he realizes the importance of his narrative, giving him the motivation to articulate his journey and perspective.