I understand the rest are discussed and documented as well, but why is the focus on the Holocaust so disproportionally focused on compared to other human atrocities? What makes industrial capacity for murder any different or crueler than chopping off someone's head for a game or shoving an iron rod or fire rockets up a woman's vagina?
I would challenge your assertion that education is "always" focused on the holocaust, and not the other ones. At the very least it depends on where the education is actually taking place. As /u/keyilan points out, students in China probably learn more about Japanese atrocities there than German atrocities in Europe. If you are from a country with stronger European ties (or even a European country), it's really not that strange to give more attention to the more local subject.
I teach history in Norway, and at least the history book that is used at my school doesn't only focus on the holocaust. The World War Two section has parts about atrocities on the Eastern Front, the holocaust, Allied terrorbombing/firebombing and Japanese atrocities in Asia. The holocaust part is larger than any of the others, but that's not really so strange considering some Norwegians were caught up in it.
History teaching isn't really about finding the "most cruel", but the most relevant and relatable.
As a follow up question, or rather clarification: In what way do you feel that the education is in fact focused on things like the holocaust rather than those committed in Africa or Asia? I assume by your question you grew up in a country in which this was the case. However for people growing up in Nanjing, the Japanese atrocities are more represented than Nazi Germany's.
So are you just speaking in terms of Western education? Or do you have the impression that it is globally so unbalanced?