There were centuries of organizations that tried to prevent war by trust and cooperation. Before the UN was the League of Nations, before the LoN was the Concert of Europe and there were undoubtedly countless efforts prior. But they all failed completely abysmally. Do you know the one thing that actually worked? Countries having nuclear weapons. Suddenly there was a strong self-interest in avoiding war, and "real" war essentially disappeared - at least between nuclear powers.
And I think that's generally true in everything, everywhere. The reason you can walk down the street safely in most places is not because of an implicit agreement of cooperation, but simply because we're all working in our best interest. You don't even consider messing with other people, because you'd just end up in prison for negligible gains. And indeed as soon as that threat and imminence of harsh consequence disappears, it suddenly becomes much less safe to walk down those streets.
BRICS is not united in some ideological conformity, but instead in self interest. They don't want to be dominated by a single hegemon. And I think this form of cooperation based solely on self interest - is far more likely to persist and yield fruitful results. I also expect this is why agreements will, and should, take much longer. Instead of just bum-rushing some virtue filled "Treaty of Whatever" that'll get scrapped by any participating government when it becomes inconvenient, they want to ensure there are implicit self-interest motivated systems driving cooperation through any foreseeable circumstance.