It is the way our brains are hardwired - to use the current expression - to be susceptible to superstition. If you have the time to trawl through the New Scientist news page then you'll find links to the original research articles. Superstitious beliefs have an evolutionary viability - it'll be something to do with will and determination as opposed to despondency and pessimism, no doubt. You could argue that superstitions do no harm as long as one recognises them as such.

When we worked on a paint additive in 1968 that was intended to preserve the same viscosity of oil-based paint from the top of the tin to the bottom we didn't know that we were inventing non-drip paint. (There were three of us and I was the cabin boy type figure). If we'd told people about non-drip paint, at the time, if they'd been interested, they would have described us as nuts. Now everybody uses it. Same with swirled crops.