Um. Because it’s bad for them.
There are many other methods of obtaining mindfulness that do not require lying. Spirituality is merely a ‘pseudoscientific’ term for ‘mindfulness by self deception’.
We all need mindfulness. We all seek it by different means. It turns out that the worst possible means is religion.
https://www.quora.com/Why-are-more-people-not-drawn-to-spiritual-practice