Why can’t we set up another international?

Because there is no powerful revolutionary state to fund it. The obvious one would be China, but they have a strict non-interference policy. The CI was the brainchild of the USSR, and like others have said, it had mixed results. I can't remember exactly where I read this, but China stopped funding foreign parties because they looked at their books and basically the parties they were funding were not getting results for the amount of money they were pouring in and needed it for their own national development.

What fucks up the internationales is trying to be one version of communism. Maybe if people accepted each other the workers could actually unite and do something useful instead of having a wank.