You do realize that the gassed were never incarcerated as prisoners. The were selected as soon as they got off the trains and gassed immediately. Those that were left were kept alive as a forced labor workforce. i could see that Himmler would be getting a bit concerned about their slave labor dying at too high a rate.
Indeed, in the concentration camp system - as opposed to the death camps - between September 1942 and April 1943 the number of prisoners doubled, from 110,000 to 203,000. This followed Himmler's agreement with Thierak concerning the liquidation of the asocials through work in Himmler's camp system and Himmler's increasing focus on using the prison population for labor. (Longerich, Heinrich Himmler, p 687) Pohl had revamped his organization into the WVHA in spring 1942, "To ensure better utilization in the camps" for which he was responsible (Hilberg, p 924), which included Auschwitz and Majdanek, directly under the Camps Inspectorate (Glucks' organization) but not Chelmno (established by Reichsstatthalter Greiser) and the AR camps (subordinate to Globocnik reporting directly to Himmler). (Pohl's apparatus, however, claimed jurisdiction over the loot taken in the AR camps from victims.) "The exploitation of the inmate labor supply," wrote Hilberg (p 925), "now became the very reason for the existence of the concentration camps." A serious labor shortage in the middle of 1942 prompted this new policy; "The labor shortage became a crisis in the second half of 1942" (Blatman, The Death Marches, p35) as the number of available German workers shrank, Soviet POWs were killed in massive numbers, and the Germans undertook a series of actions, including forced labor for foreign workers, to increase the labor force.
Thus, the Nazis sought to expand the labor force through Sauckel's "recruitment" and forced labor programs effort especially in the occupied territories (Sauckel's appointment as plenipotentiary for labor came also in 1942, in March) and expansion of captive labor programs under Himmler, all these labor-focused efforts during 1942, the time of the quotation attributed to Himmler.
The concentration camps were an increasingly important source of labor beginning in 1942 and then massively so after that, and the authorities took steps to ensure that the inmates were available for work. They not only increased the inmate population as noted, but they also tried to go a bit easier on inmates thereby making those in the camps reasonable facsimiles of productive workers. In a circular issued by Glucks to all camp doctors on 28 December1942, during this period of increasing prisoner population, Glucks explained clearly the purpose for "relaxation" of conditions and the goal of reducing deaths: "The best doctor is the one who maintains the capacity of inmates to work at the highest possible level. Now more than ever before, camp doctors must keep tabs on the diet of the prisoners. . . ." (quoted in Sofsky, The Order of Terror, p 321) On 20 January 1943, Glucks issued another circular on the topic, "I hereby make all camp commandants and directors of camp administration personally responsible for maintaining the working capacity of the prisoners." (quoted in Sofsky, p 322)
I know what deniers want to say and how they try to use this quotation, conflating concentration camps and death camps - Himmler decided to stop killing so many inmates, they say, presto no Final Solution - but there was no conflict between the policy of reducing deaths in the concentration camps, to expand the labor force, and the Final Solution, to exterminate other prisoners as Jews. The prisoners referenced in Glucks' circulars, for example, were those in the camp system, not those selected for extermination. That said, the labor policy extended to some Jews as well as to the concentration camp prisoners, in Goebbels famous formula whereby about sixty percent of the Jews were to be liquidated and "only forty percent can be put to work," for the time being.