The UN doesn't focus on every other country in the world because no other country in the world is occupying a territory it has no claim to and randomly destroys the infrastructure of the occupied territory and uses lethal force against its people.
source: I heard an ex-Israeli soldier who is proud of his country speak about this at length. http://www.breakingthesilence.org.il/
The most trivial comparable criteria is probably the number of casualties in the conflict. If you look at the number of the Palestinian casualties during the Israeli-Arab conflict, and compare it with the number of casualties in any other conflict in the world (such as US's war in Iraq, NATO's war in Kosovo, The war in Syria, The massacre in Sudan, and sadly many other places), you'll see that the Israeli-Arab conflict is far less deadly than those any other conflicts. If only the UN would have given all the other conflicts in the world as much attention as it gives the Israeli-Arab conflict, many people's lives would have been saved. But the UN doesn't. That's probably because the UN's committee of human rights is controlled by states that, let's just say, don't care too much about human rights.
By the way, the organization you linked to is considered biased and unreliable in Israel. This organization "collects" evidences about supposed crimes that Israeli soldiers supposedly committed, but mysteriously refuses to share those evidences with any authority in Israel, despite requests from the legal authorities for such evidences in order to open an investigation and put the soldiers to trial. This organization claims that it has evidences for supposed crimes, but instead of passing those evidences to enable the trial of those who committed the crime, the people of the organization prefer touring around the world telling fishy horror stories, while trying to generalize and present all the Israeli soldiers as criminals. Reasonably, this raises an eyebrow or two about the reliability of those stories.
UN fixation on Israel is just another symptom of the rotten nature of UN, a mix of antisemitism and autocratic governments and UN bureaucrats.