My 12 year old nephew asked me something once. He said "if there is a God, why doesnt he just show up in the sky and tell everyone he exists?"
Thats a pretty damn good question if you ask me. Some will say that "well, its because God wants us to have faith, or test our faith". But why would an all powerful God provide us with reason and logic, and then expect us to ignore both in order to believe in something for which there has never been any tangible evidence or proof?
I think the prevalence of religion, be it Hinduism, Monotheism, Scientology - whatever, is because people just want to believe, even if there is no proof. People just want to believe that there is some greater meaning out there, even if there is no reason to believe there is.
Remember, even the earliest human civilizations had belief systems which explained the great unexplainable (i.e. death). We now scoff at these "pagan" beliefs, but really, what makes the belief in Zeus or Amon Ra, any less plausible than a belief in Allah or God?
Wanting/needing to believe in something seems to be a human imperative, because the alternate -essentially, meaninglessness - is something humans cant come to terms with.