1. The concentration camps that built prior to Treblinka, Sobibor, and Belzec were intended to put the Jewish people to work.
The Nazi party acknowledged that many of the Jewish population had a strong skill set that can provide economic benefit for the country and they take advantage of them using concentration camps. Trblinka, Sobibor, and Belzec on the other hand were made to kills/execute Jewish people.
2. The Nazi party tried to maintain the secrecy by ensuring that only high ranking officials know about the plan.
The nazi party aware that openly announced the plan for the mass killing of the jewish people would caused a strong opposition from many people in Germany. Because of this, the party only tell the plan only to a select few that the party could fully trusted and masked the act of mass killing as some form of ideological restoration.
3. Because Germany cannot passed through England's armed forces
The madagascar plan was made to rellocate the Jewish people that the Nazis capture to the island of madagascar. To transport them, Germany had to passed the area that controlled by British Royal Navy and air forces. The Nazis acknowledge that the British would be too strong to handled so they decided to abandoned the plan.
4. Because Hitler considered some of those individuals as 'honorary Aryans'
Hitler acknowledged that there are several Jewish individuals that contributed a lot to Germany during the world war I. The people who were acknowledged by Hitler were given the title of 'honorary Aryan' and can escape the brutal treatment that the country gave to the rest of Jewish population.
