The simple answer to the red bit is it gives many people "comfort" to believe there is a greater power at work and that their lifeforce isn't just extinguished (most people have difficulty with the concept of mortality).DB10's reply contained quite a bit about comparative religion, but I expressly want to stay away from discussing religion.
At this stage I want to concentrate on 'belief'. i.e. Why believe in any god or gods?
My intention in mentioning the tens of thousands of different religions and their thousands of sub-sects was to highlight the improbability that any one of them is true. It then follows I think that it is reasonable to conclude that none of them are likely to be true.
To pick up on some of the above posts about children; Q: How do you get a child to believe something? A. Tell them it.
Children innately believe what adults tell them. Years ago I told my daughter's classmates that their teacher was 168 years old. When one solitary kid expressed surprise I explained that she was born before electricity was invented and that convinced him. It was quite a while before they were convinced that she was only 48.
When we are young we believe in Father Christmas, the Easter Bunny, the Tooth Fairy and God (s). As we get older we discover that there is reliable evidence to suggest that the first three don't exist and no convincing evidence that they do. We therefore stop believing in them.
So why don't we apply the same scepticism and logic to god? The same scepticism and logic that we utilise in the rest of our lives.
Maybe fear (Hell is pretty scary). Maybe the social elements of religion. Maybe it's just the quantity of unsubstantiated stories involved or the administrative structure of religions.
I don't know, but I'm sure that if believers applied the same standards to their belief in god as they do to the Easter Bunny etc they would come to the conclusion that there is no more evidence to support one than the other.
The blue bit above is another classic inaccuracy that many atheists postulate. Something being called by a different name in a different culture does not "prove" only one (or none) of those things can exist. Excuse the overly-simplistic example but, a car is a car. One car is a Nissan, another a Ford. Does that mean one of them must be named incorrectly and thus none can exist?