Because so many couldn’t possibly fathom the depths of depravity that awaited them (I mean who could even imagine it) - the persecution of them was a slow steady drip some people had the foresight in the 30s to emigrate but then when people started losing their jobs and having to walk around with visible identifiers (because not all Jewish people looked stereotypically Jewish) - people who were known in their communities as Jewish couldn’t suddenly change their names and visibly Jewish people (Orthodox) couldn’t hide. There were a lucky few who were able to hide but not many (and how frightening for them that they could be found out at any moment). If some of these people could have seen what was coming - some would have moved to places where no one knew them and shed their visible identifiers and names, some would have emigrated and still some would have stayed.
For a comparator - in the Rwandan genocide many Tutsis were only identifiable by their neighbours knowing they were Tutsi (similar to many Jews) and hence they were unable to escape their fates but someone from outside the region would be unable to distinguish between a Hutu and a Tutsi objectively.
Regardless - there are no words for how evil what happened during the Holocaust was but that is not the discussion DA was having. It’s alright because people don’t want to acknowledge a difference of experience in the present - and that’s fine - we get it.