The religion was the key really. Most other ethnicities didn't have true religions in the modern sense of the word. The gods were just entities that they believed were there.
To the Jews however their religion was everything. It was central to their being who they are.
Leave things without religion and people will be inclined to think logically- why should I stick to my ancestral beliefs and all that silly stuff when I can just move to the city, learn that other language and have a nice life? With a religion they're given a reason to stick to things.
The Roma as an interesting and notable exception.
To the Jews however their religion was everything. It was central to their being who they are.
Leave things without religion and people will be inclined to think logically- why should I stick to my ancestral beliefs and all that silly stuff when I can just move to the city, learn that other language and have a nice life? With a religion they're given a reason to stick to things.
The Roma as an interesting and notable exception.