It's just the way of things. The only way to keep aggressors at bay is to project power, which is why every nation has police forces to ensure order. But there's no world police force, so nations must make do in other ways. And so the more powerful nations decide on the rules that all must in theory follow, and they also decide when they themselves can break those rules. It's why so many nations want their own nukes.

The "big boys" involved in the Ukrainian issue are America, Russia, and Germany. Germany is still too timid to act (owing to the war), and America and Russia still have ideological cold warriors in their government apparatus.