Because religion came first.

The only reason why religion is so deeply rooted in our society, is because it came first.

What do I mean by that? I mean that our ancestors used religion as a means to explain things that were unexplainable to them at the time. For example, why did people get sick and die? Why are there so many natural disasters like floods, drought, famine, etc... Our predecessors had no way of explaining these natural occuring phenomena, so they used religion to explain it. "Oh God is the one who made this man sick, cause he sinned." etc...

But now with rational and logical thnking, we have managed to break the code. We are now better able to explain these natural occurences. For example, we now know why people get sick. It's because of germs and viruses. We now know why there are natural disasters. But still religion is deeply rooted in our society because it came first.

Imagine what it would be like if science came first. There'd possibly be no room for religion to grow and develop. In fact, it'd be considered absurd and silly to blame these natural occurences on a "higher power".

Still, in anycase, religion will remain around for the next several centuries, or even forever. Until we can prove that there is no heaven or hell.