Here's why:
* The conflict is not solely about one individual. The book explores the animosity and prejudice that exists between the two groups, and how it leads to tragic consequences.
* Both groups have their own antagonists. The Socs, as a group, are antagonistic towards the Greasers, representing wealth, privilege, and prejudice. Within the Greasers, the character of Darrel "Darry" Curtis is often seen as a more specific antagonist for Ponyboy, as he is strict and sometimes harsh, leading to conflict between them.
* The true antagonist is societal prejudice. The book uses the rivalry between the Greasers and Socs to explore themes of social class, poverty, and how these factors can create conflict and violence.
So, while there are individual characters who contribute to the conflict, the true antagonist is the societal division that fuels the tension and leads to tragic events in the story.