> Because the Holocaust can refer to either the Nazi's genocide of Jews or all the genocides carried out by Nazi Germany. Most often it is the former.

This is not counting all the genocides by the Nazis. This is just counting the people murdered in the extermination camps and on their way there.

If you count all the other Nazi genocides you get tens of millions, e.g. targeting of civilians during the Siege of Lenin Grad, the Dutch Famine, etc.