In the modern world in which virtually all services are marketable, one may wonder why Taoists Masters refused to teach their art of deep meditation. Isn't it just technique?
Taoist meditation can really be treated as a technique with different applications depending on which direction as well as how far one ventures into. In the modern world, even spiritual healing has been replaced by psychological or psycho-therapeutic treatment. The mentality of the modern man is "What is the problem?" and then "What are my options?"
Not so for the early Taoists (or Buddhists who practiced deep meditation as a route to enlightenment). Some of my readers may disagree with me: I didn't see much beyond meditation techniques in Taoist meditation. Let me explain.
The best way to approach this issue is still the modern man's strategy, in this case: what was the problem facing the old Taoists that motivated them to pick up the practice of deep meditation. Immortality of the physical kind had been raised as the problem, but that certainly failed to convince unless we believed that old Taoists were simply stupid! OK, the next contender is "spiritual immortality". That failed also for the majority of the Taoists, because most practitioners would presumably understand that only a very small handful of practitioners got into that arena. Was there a more worldly objective to be achieved?
I believe we can understand the subject better from a religious perspective. The overt stages of Neidan (Taoist deep meditation) practice are firstly, cultivate essence to Chi (煉精化氣), secondly, cultivate Chi to spirit (煉氣化神) and finally cultivate spirit to Void (Tao) （煉神還虛). In chi-meditation it can be said to cultivate one's body, train one's mind, and then mind/body back to void (Tao). The question is: what is Mind/body back to Void? It can be interpreted as becoming an spiritual Immortality, or it can have sound practical meaning.
According to Grandmaster of Wu-Liu group Immortal Wu chongXu (伍沖虛) the initial stage of one's route to enlightenment if to be able to experience the Void (Tao), even before the first stage! What is this enlightenment experience? In Christian lingo, its like "love thy neighbor as thyself", in Buddhist lingo its like "Every perception is illusion, instead of absolute" (凡所有相,皆是虛妄 - Chapter 5, Diamond Sutra). In short, master Wu's teaching was for those wisest people (大乘人) who were fully enlightened, and who wanted to have a "personality overhaul" so that they could achieve body and soul being fully (and continuously) enlightened, and that they could keep this total enlightened state in their daily lives as well as having the conviction that they could retain their total enlightened state after death. What is the state of being body and soul fully enlightened? It is like someone who can also perform "love thy neighbors as thyself", without bearing any grudge.
No wonder the Masters refused to teach their deep meditation techniques to more common folks, who wouldn't need those techniques anyway!