Why do atheist jews exist? (question from a non-jew)

Hi all! I am from a christian background and visited Israel. Loved it. I was just looking around the jewish subs

I was listening to Sam Harris (an author who actively criticizes islam), and when asked about why he doesn’t attack judaism the same way, he explains that he has met many jewish rabbi’s that don’t believe a God that actively listens to prayers. Sam also explains that one can be atheist or accept the possibility that there isn’t a God but you can still identify as jewish.

Is this true? and why is this so? Is there a passage in the old testament that says that Judaism is flexible and jews can discard parts of it?

For the podcast itself, see below:

https://www.youtube.com/watch?v=MF2_b_2xHlw