Why did Hitler attempt to complete the Holocaust during WW2?

What is important to understand in regards to this question is that first, the underpinnings of the Holocaust did begin before the war, and second and perhaps most importantly that there could be no victory in the war under Nazi ideology without the extermination of Jews. They did not see Jews as "loyal Germans/workers" and far from using a huge portion of their war resources, Nazi Germany hugely enriched itself through the economy of mass murder. First by stealing all wealth and possessions held by Jews inside and outside of Germany, secondly by employing Germans in the military and in the mechanisms of extermination such as as guards, and third by exploiting the slave labor of both Jews and gentiles under their control. A report from Odilo Globocnik, the man in charge of the Operation Reinhard death camps which were responsible for at least a third of the deaths during the Holocaust estimated that in these camps and the labor camps in the Lublin district which he controlled alone, he had extracted nearly 200 million Reichsmarks. This is likely a low estimate since Globocnik is known to have kept a great deal of wealth for himself and his associates. This is also only for a portion of the wealth extracted from Jews, and doesn't include wealth extracted from other other groups such as Roma or that of other slave laborers. The Nazis also did plan to keep a minority population of Jews alive for the duration of the war to be exploited as slave laborers.

It is however a misnomer, and can indeed be a failure of both empathy and of understanding of Nazi ideology to paint the Holocaust as an economic, tactical, or indeed as a logical endeavor. Genocide is not logical, and it should not be painted as an economic necessity.

Although historians debate as to when Nazi ideology became fully hinged on total extermination of the Jews, it certainly came about by 1941. On January 30, 1941, Hitler said this in a speech at the Reichstag. By December 7, 1941, with the entrance of the United States into the Second World War, the world was again at war. However, the full scale extermination of the Jews had begun months earlier, with the Nazi invasion of the Soviet Union in the summer of 1941. The Einsatzgruppen who were employed when Operation Barbarossa began murdered at least 1 million Jews through mass shootings, mainly in Eastern Europe. However, oppression, violence, and even murder against Jews began much earlier. Street violence against Jews by members of the Nazi party began even before the Nazis came to power in 1933. The 1935 Nuremberg Laws curtailed the basic freedoms of Jews and took away their citizenship in Germany. In 1938 a large pogrom, called Kristallnacht was enacted against Jews in German controlled territories. Antisemitism was rife in non-Nazi occupied countries as well but most did not see nearly the levels of violence as Nazi Germany. All of this shows a pattern of oppression of Jews outside the context of war. This was about ideology and power, not a tactical move in wartime.

Once the war began, by invading Poland, Nazi Germany took control of the largest Jewish community in continental Europe. Some three million people, over 90% of whom would be murdered. It is no coincidence that "Eastern" or "Polish" Jews were particularly reviled even in Nazi propaganda of the 1930s. Once they had control of this population, their ability to actually engage in mass extermination of Jews based on pre-existing ideology was heightened. At this point, the oppression against Jews in occupied Poland began to heighten and heighten, planning for wide spread mass extermination was underway. Essentially, the war created the possibility for the Nazis to enact the most extreme version of their preexisting ideology on a massive scale. Murdering all the Jews in Europe would have been impossible to imagine without controlling a great deal of territory, and a great deal of Jews. That meant expansionist warfare. This was seen by some among the Nazi high command as tactical, as they believed Jews were a political threat for their imagined association with communism, others saw it as economic because they say Jews as economically violent, and because they imagined Jews as wealthy they saw stealing from them as a "good" economic move. However each of these so called "tactical reasons" for genocide were in their essence ideological because they were based on the Nazis own antisemitic ideologies about Jews, not on reality.

https://www.yadvashem.org/education/educational-videos/video-toolbox/hevt-nazi-ideology.html

https://encyclopedia.ushmm.org/content/en/article/victims-of-the-nazi-era-nazi-racial-ideology

https://www.facinghistory.org/holocaust-human-behavior/himmler-speech-posen-1943

https://www.jewishvirtuallibrary.org/hitler-s-threats-against-the-jews-1941-1945