Modern clinical mindfulness has a documented origin and a deliberate design, and neither is a secret.
Jon Kabat-Zinn established a stress reduction clinic at the University of Massachusetts Medical Center in 1979 and built the programme now known as Mindfulness-Based Stress Reduction: an eight-week course, weekly group sessions of two to three hours, one day-long retreat, and daily home practice with recorded guidance. Its core components are a body scan, sitting meditation, and gentle movement drawn from hatha yoga. He was explicit about the strategy. The practice was presented in secular language so that it could enter a hospital, and the Buddhist terminology was removed as the condition of entry rather than because it was thought dispensable in principle.
Mindfulness-Based Cognitive Therapy followed, developed in the 1990s specifically to prevent relapse in recurrent depression, and it is the version with the strongest evidence behind it; it appears in clinical guidance in the United Kingdom for that indication.
The wider spread ran well ahead of the evidence. Mindfulness entered schools, prisons, armed forces and corporate training programmes, and application-based delivery now reaches an audience of a size no trial ever contemplated. Researchers within the field have published sustained criticism of the resulting overclaiming, and the standard formulation inside the literature is that enthusiasm has outrun the data. That criticism comes from the people running the studies, which is the reason to take it seriously rather than to discount it as hostility from outside.