What is it about Christianity that actually has positive impacts on society (without using some sort of mystical nonsense as an explanation)? Why are people less Christian now than before (without saying jews)?

These answers should be self-evident by now.

Tradition provides solutions for problems we have forgotten. Those solutions have been forged through great pain and the collective knowledge of hundreds of generations, which makes it impossible for any individual to truly comprehend the entirety of traditional systems. Christianity is intrinsic to the spirit of the west and fundamentally inescapable for its people, just look at progressivism which is a perverse atheistic version of Christianity.

People have lost their faith due to progressive Deleuzian territorialization. Society is no less religious, but their values have been completely inverted as demonstrated best by the overt celebration of the deadliest sin: pride. In order for the progressive heresy to assert itself, it had to simultaneously dismantle the power of the traditional church institutions, which is easily seen in how progressivism is the only religion legally allowed to be taught in school.