I think he found the Holocaust of such evil magnitude that he just couldn't bring himself to treat it directly, which is why he used the form of a horror film to treat it indirectly.
Mislim da je Holokaust za njega bio toliko užasan da se nije mogao privoliti da se odnosi prema njemu direktno, zbog čega se koristio nekom vrstom horrora kako bi se odnostio indirektno.