Considering the purpose of the Operation Reinhard camps, why would their closing in 1943 be so surprising?

In the fall of 1941, Nazi Germany implemented a plan to systematically murder the Jews in the General Government. This plan was codenamed “Operation Reinhard.” Three killing centers were established as part of this action: Belzec, Sobibor, and Treblinka. Operation Reinhard marked the deadliest phase of Nazi Germany’s intention to commit genocide against the Jewish people.