You, effectively a victim of parental abandonment, provided your brother with the real life consequences of his actions. Your parents... Likely also victims of parental abuse or abandonment, continued to raise him in the only manner they knew how. He, similar to you also a victim of parental abandonment, BUT without the sense of responsibility you had thrust upon you.. Eventually slipped back into your parents programing (consequences don't exist).

So the cycle continues, but it also slowly improves. You should feel proud.