Because all the other sites get their information from the old debunked Shettles idea and you can read about that in the "Trouble with timing" essay. We operate under a different paradigm here based on newer science - the Trivers Willard Hypothesis, the Maternal Dominance Hypothesis, and blood glucose levels. The other swaying theories only appeared to work because they sometimes mimicked the circumstances that actually swayed (like eating lots of meat does tend to sway blue).