Final answer:
Randy decides not to participate in the rumble because he feels it won't change anything, highlighting the futility of the violence between the Greasers and the Socs.
Step-by-step explanation:
The character Randy from the novel The Outsiders by S.E. Hinton decides not to participate in the rumble for a very significant reason. His decision is not based on fear of arrest, concern about who would win, or fear of getting hit by Dally. Instead, Randy's choice is reflective of his realization that the ongoing feud and the resulting violence between the Greasers and the Socs are ultimately futile.
The correct answer to the question, 'Why did Randy decide not to participate in the rumble?' is B) He said it didn't matter because it wouldn't change anything. Randy understands that the rumble won't solve the deep-seated issues between the two groups, and it certainly won't alter the socio-economic divide that fuels their conflict.