I think that's because the term "concentration camp" is so heavily associated with the Nazi extermination programs. Likewise, there were Nazi concentration camps that were not designed to kill their occupants, and they're sometimes referred to as "labor camps".
"Auschwitz seems to overshadow all the other camps. It also captures our attention because we know a great deal about it. ...It was the only death camp (Auschwitz II) that was also a large slave labour camp (Auschwitz I), with the result that tens of thousands of slave labourers, having endured selections, random violence and the death marches, survived to bear witness to genocide."
"Most of those killed in the Holocaust were not inmates in concentration camps."
"Much of what we have come to see as the particular moral debasement of the concentration camps was absent in the death camps."
"[Extermination] camps were grotesquely efficient: Sobibor murdered about a quarter of a million people, a quarter as many as Auschwitz-Birkenau in one three-hundredth of the space and half the time. Precisely because of this efficiency, we know relatively little about the dead. There are only three survivors’ accounts from Belzec, where, between 17 March and late December 1942, 434,500 Jews were murdered. As Primo Levi said, we know little of those who were truly at the bottom."
"Conversely, much of the story of the concentration camps does not overlap with that of the Holocaust. The camp system was a latecomer to the project of genocide. There was no representative of the KL [concentration camps] at the Wannsee Conference [which organised the Final Solution]. It was only after the conference that Himmler decided the camps could play a big role, not primarily as sites of immediate extermination but as reservoirs of Jewish slave labour. Only towards the end of the war, as Wachsmann points out, did the majority of Jews find themselves in camps and only for a few weeks in 1938 were they the majority of registered inmates."
