I don't see why any rider shouldn't be able to help out a mate on another team, regardless of nationality, if it harms their own race they have to answer to their DS anyway.
Because it is an unfair advantage from the perspective of those who did not benefit from the help. It is a race after all, and to use a sport metaphor that doesn't exactly fit, the goal is to have a level playing field.
Because it is an unfair advantage from the perspective of those who did not benefit from the help. It is a race after all, and to use a sport metaphor that doesn't exactly fit, the goal is to have a level playing field.