I have been thinking about this for a while, and I realize that I know it isn't like the whole world is made of atheists, so there are still people who believe in God. However you can't be a christian like they were 2000 years ago or like they were in the middle ages. It just isn't as powerfully reinforced by the community like it was back then. Some places like Texas try to ban the teaching of Evolution in favor of religious propaganda and Florida was like that for a while too, but the kind of Christianity where Jesus is the son of God, born of a virgin died and was resurrected, that is as dead as the samurai.
You can't be a samurai warrior any more either. You could try to pledge allegiance to a person and live by a code, but being a samurai like they were in the middle ages meant being something more than that, your whole way of life and belief about your purpose in life was reinforced by a huge community that supported this belief system and life style. People can try all they want to but it will never be like what it was in the middle ages.
Now a days, we have tremendous amounts of scientific explanations for our creation, and the general fact is you can't prove the existence of God. Back in the middle ages, it was different, people really felt you could prove God existed and they had this huge community they were part of to reinforce their belief system, and even purpose in life.
I think Christianity started to lose its mojo when other religions started getting mixed into the communities. Also, scientists verified that Christianity as an absolute system that can explain everything, isn't verifiable in some cases and is wrong really in areas like the Sun going around the Earth and everything in the heavens going around the Earth too.
And that is the way it is.