Tired of all the hazing the only one who toughed it out went through it all. Made more effort to be kept out feeling like, he didn't matter, or belong. Asking himself, "why did he stay," they obviously didn't like him, and he didn't always agree with how things were handled. Another made up standard to live up to when they didn't have it together.
He had another life before they crossed paths they can't take credit for him and all his efforts. They can't tell him, how to feel, or think.
They dk what's going on in his head. He may not argue, say much but refused to let them take advantage of his kindness. Once he spoke up that's when everyone kept him out. Before they'd taunt him, let him think, he could be one of them. He was okay and moved on. No reason to stay felt it wasn't worth it anymore.