German efficiency led to industrializing death.
Muslims prefer bloodier, less efficient methods.
They had to depersonalize the process because it was making too many concentration camp staffers sick.
They initially tried various inexpensive methods. The original method was to dig a big trench, use whips, clubs and dogs to line up Jewish men, women and children along the edge of the trench, and mow them down with machine guns. This was too upsetting for the people who had to do it. These problems were brought to Himmler and Heydrich, who realized that they had to turn mass murder into more of a mechanical process.
That's why they had to spend money on capital equipment like gas chambers, ovens, etc. The psychological effects of inexpensive, personalized murder were causing inefficiencies.
That's also what led to the use of prisoner units, or Sonderkommando to actually do the physical work of moving the bodies, stacking the bodies, cremating the bodies, washing out the ashes into pits, etc.