Back to my dear unicorn guardian: why I believe in him is irrelevant, what matters is if he's real. If I believed in the unicorn (or should I write Unicorn? I don't want to be blasphemous!), I'd probably have the same reasons as the other believers: he'd give me a sense that I am not alone, that somebody cares about me, that's somebody listens when I pray, that I'll be rewarded for doing certain things. It would really help me on an emotional level, just as Jesus helps other believers - emotionally.
But again, why should it matter what my reasons are? What matters is if the Unicorn is real or not. Conversely, it doesn't matter why people believe in Christianity, Islam or other nonsense, what matters is whether these things are real. And if they were real, there should be hard evidence, otherwise it's just that - a made up story, a hoax, a myth.
How exactly do you know that the spiritual or divine does not exist? You are so sure, but why are you so sure? Hard evidence DOES NOT need to exist for something to be real. We might not have found that evidence yet. There was no evidence a thousand years ago for many things that we now know are real. Just because we don't have hard evidence of the divine currently does not mean it doesn't exist.
And your analysis of why people believe in God is so far off that it makes me wonder if you have ever even talked with a believer?
Edit: and the reason why someone believes what they do, rather than the belief itself is important specifically because we are dealing with things that are currently unable to be proven or disproven so the logical aspect of the "why" is important.