I've always assumed it's a kind-of safety net for people who don't want to take ultimate responsibility for their own decisions, or something.

Believing in a higher power maybe gives them comfort that other things will get taken care of. Kinda like when you hire a cleaner and you don't have to worry about having a dirty house anymore. Relieving some pressure on your brain, or something. Appealing for some I guess!

The way I look at it is nature is way more complex than we humans understand. Facts are facts but science is the interpretation of facts. Sometimes scientific theories are wrong. Obviously some of religion is wrong, since multiple religions conflict on ideas. So, where does that leave us hopeless and confused. or you can have hope and believe there is more to life and the world than atoms and protons.

Fear of their own mortality is the answer...