It matters what you believe in Christianity because it is a religion of faith and belief. If you no longer believe in God, you're not a Christian, you're an imp

It matters what you believe in Christianity because it is a religion of faith and belief. If you no longer believe in God, you're not a Christian, you're an impostor. But Jewishness is decided by whether you were born Jewish or converted to Judaism. If either of those is true, you are a Jew, regardless of what you believe. None of the laws are predicated on believing in God (the one I mentioned before from the ten commandments precludes believing in other deities, but apparently permits atheism). What makes someone a "bad Jew" is failing to practice Judaism. But there's no incentive to conduct a witchhunt over it, so there's no incentive for rhetoric about the importance of belief. I belong to a Conservative synagogue and I have never heard a sermon about the importance of believing in God. It isn't important. Ethical behavior is, and that is the content of our sermons. It may be difficult to see a point to practicing if you don't believe in God, but, again, I know people who find value in the symbolism and the ritual and the religion's capacity to shape ethical behavior despite not believing in a supernatural being or origin. The entire Reconstructionist movement teaches that Judaism and the Bible were created by mankind. It may be a small movement, but it is real thing, and I know Conservative Jews who are atheists but still get value out of the practice. I'm sure you will be able to find a marginal rabbi (probably "Orthodox", a self-applied label by a movement younger than the Reform) who will activate your confirmation bias. But I assure you, things are different outside your experience.