Initially, in evolutionary terms, it was due to ignorance - being unable to explain natural phenomena by natural means - and I dare say that still prevails in parts of the world where people are still primitive, in the anthropological sense of that word. However, as societies become less primitive, the real ‘engine’ of this desire to believe in a supernatural world is the psychopathology of the individual in question.
The word ‘psychopathology’ is used accurately, because belief in a god or gods fulfils the diagnosis and aetiology of psychosis, as described in the ‘Diagnostic & Statistical Manual of Mental Diseases (TR IV)’.
Anyone who does not accept this fact has only to substitute the words “the Invisible Pink Unicorn” in their so-called ‘holy book’ in place of the name of their god, and then go around claiming that the IPU created the cosmos et al; they will rapidly find themselves incarcerated in an institution for the care of the mentally disturbed, even though they are saying and doing nothing other than any other theist does.
Furthermore, any psychiatrist will confirm that one of the most intractable mental illnesses to deal with is psychosis, which explains why most theists are totally resistant to rationality. Unfortunately, this means that often the only hope for those who are afflicted with this particular illness is long-term treatment with anti-psychotic medication.
The only people who proclaim that they are theists who are not psychotics are those who are simply exploiting those who are! However, even they must take care; after years of pretending to believe in that irrational and unsubstantiatable nonsense, the chances are that they, in turn, will develop psychosis too!
Unquote.Fortunately, Risperidone is a uniquely effective anti-psychotic used to great effect in dealing with delusional psychosis. Unfortunately, most psychotics do not want to take it of their own free will, so it has to be administered to them, often with some measure of compulsion.