Hey! A question right up my alley!
I can only speak for the US and to some extent, Europe. First, the Holocaust devastated many Jews, turning some into stronger Jews but many into outright atheists or, at best, questioning agnostics. How many times can God devastate a people yet expect them to remain worshipping him?
As stated above, Judaism is an orthopraxy religion. It’s about right practices more than right belief. In a weird way, Judaism doesn’t require one to believe in God but to obey His commandments. Questioning God is a very Jewish thing to do.
Enter America where for most likely the first time, Jews were able to live out their Judaism as they saw fit. No more Ghettos and pogroms and forbidden professions and Jews became worldly citizens…like most everyone else. What on earth is the reason to keep Kosher nowadays? Many still obey the laws for multiple reasons but just like general society, belief in God, belief in the reasons to obey the Laws of Moses, belief that we are a Chosen People just clashes completely with American life. In order to continue to practice as an obedient Jew, they need to self isolate to some extent and can not fully participate in American society…so, many don’t. Some still believe in God. Some don’t. Some leave the culture behind completely (me) and some still participate…and call themselves Jewish Atheists.
I grew up immersed in Judaism and left it all when I lost my faith in God. There was no point, in my mind, to continue the cultural aspects when I felt much more American that Jewish but others enjoy walking within both cultures.
I’m not sure I answered anything, but it is definitely true that many Jews no longer believe in God or, if they do, continue to be pious Jews. There are still many that do, however. We tend to model the same patterns as Christians except that we have the choice to remain in the community or not.