On a nation level the power of a court to prosecute individuals is supported by a policing force that is capable of resorting to violence on a local level that is acceptable for the greater peace.
On an international level, enforcing justice would ultimately require going to war, with mass casualties and likely numerous incidents of potential breaches of the law itself.
In the example of Israel vs Hamas, the ICC warrant included the leaders of Hamas - but the ICC had zero chance of actually arresting them, they were killed by Israel though. So half of the defendants carried out the justice sought by the ICC on the other half.