What is the evidence that these are drug traffickers? Are they convicted anywhere? Should the police in the US be able to execute anyone they claim are trafficking drugs or committing other crimes?
..."alleged" drug traffickers. These are summary executions. The US shouldn't be committing summary executions in international waters anymore than they should be doing so on US soil.
The reason no other country is doing anything about it is because, well, what would they do? Submit a complaint to the ICC? And for what benefit to themselves?