If it were not the favorable strategy, it wouldn't have to be illegal, because it would not be popular enough to hurt consumers. People habitually favor optimizing for short-term success because there is no long-term if you don't survive the short-term. Furthermore, it is actually repeated interaction that makes collusion/cooperation better than betraying, because of the opportunity to get punished on subsequent iterations. It is this medium-term thinking that pushes collusion (but not too much of it) into a position of dominance. In the truly long term, nothing is stable because we're all dead anyway.