Why do people think Roman gods aren't real but think there's a God now?

In Roman times, as Paula Fredriksen says, “Gods ran in the blood”. The populations were all thinking that there were many gods. As time went on, and especially after the Enlightenment, people began to move away from that idea and now, when we think of ourselves as individuals, it is hard to imagine a world where everything is run by a multiplicity of gods. Monotheism, however, is not new. The uniqueness of Jews in Roman times was that they were monotheists. Ironically, the Romans called the Jews ‘atheists’ because they did not believe in the power of multiple gods. While they may have acknowledged their existence, the ONE GOD, the GOD of Israel, was the most powerful God of all.