1. The dough.
2. The requirement for unity in certain actions. While it does create problems with decisive action, and hence your obserevation of how regional organizations rise in importance, it does force the dialogue for global collective action into more depth, with disappointing results.
The biggest problem with the UN was that it permitted any dictator to be considered a valid and sovreign government.
As in, no membership without representative government.
Too bad that is not the rule. See also how Utah had to bend their laws to join the Union.