Some notes on a possible answer:
(1) If, for some evolutionary reason, our genes had a greater change of surviving as long as we believed some bullshit to explain the world instead of losing time trying to understand it scientifically, then our genes would make us believe some bullshit. Just try to think about it: our species becomes intelligent. It is a huge evolutionary advantage. However, along with intelligence, comes curiosity. We want to know who we are, how the universe works, why the world is as it seems to be. What would be the easiest path for our genes to spread? Make us scientifically curious, prone to far-fetched experiences that made us look like geeks, obsessed with scientific knowledge? Or just make us accept any explanation that made life easier to bear, without thinking too much about death, ready to be confident and happy when spreading our seed? Well, the answer is clear…
(2) So, science and rational thought are allowed by human nature but are not natural to humans. Humans tend to be irrational. Humans tend to believe what makes us happier and more comfortable with our own lives. So, if we want to get closer to the truth, we must escape the evolutionary Matrix. We must confront the dark, cold reality. And we may even survive it!
(3) The degree of emotional attachment to a specific belief doesn’t tell us anything about the truth of that belief. We tend to think it does. If we feel in our gut something is real, we will consider it real. But we should understand our guts are very poor judges of truth: they are even worse than our brains!
(4) We should never be surprised about seeing people believe incredibly stupid things. We should be very understanding. We may be believing in some bullshit too. In fact, bullshit in our brains is bullshit we can undoubtedly control, as long as we search for it. We can try to convince others out of bullshit, but what we should do first is finding the bullshit in our own skulls.
(5) Astrology, homeopathy, etc. (what a big etc. this is!) are systems with a semblance of coherence and rationality, artistically fulfilling, beautiful in their own way, made to be believed with our guts. They are rationally untenable, but our genes made us explain the world first with our guts and only then with our brains.
(6) Science does not create an emotional link between knowledge and the knowledge-bearer. It’s a problem that arises from the fact that science is a rational construction rather than an off-shot of evolution and instinct (reason is a by-product of human evolution but it’s not central to human nature). That’s why an extraterrestrial species would be very different from humans in all aspects, but if they invented science, their methods would probably be similar to our scientific method. So, we must understand this and promote science using reason and sheer curiosity.
So, people believe bullshit because our brain has no direct way of distinguishing bullshit from truth and our brain feels more comfortable with ready-made BS systems of thought than with doubt-ridden scientific knowledge. Science is hard, bullshit is endlessly adaptable to our specific needs. Do I need an explanation that makes the universe control my life? I’ll have astrology. Do I need a medicine that makes treatments painless? I’ll have homeopathy. Do I need a theory that makes the world seem contrived to make me fail? I’ll take any conspiracy theory.
That’s my explanation why we believe in bullshit. I hope it’s not complete bullshit.