It's in one group's best interest for Nazi to be a slur you can throw around with the weight of 6 million deaths behind it.

Unfortunately Socialist is a much lesser insult despite having 60 million deaths burdening it. 

From the 1901 Jewish Encyclopedia:

https://image.nostr.build/789e5672b845077d0229845c78615214c0e8dc31c4762c0202a785604013eb8a.jpg