When you ask the question as to why there are so much secrecy surrounding mysticism and kabbalah you might find that the answer by practicing Jews are simple and direct while making perfect sense too. Inside the human body a soul breathes while inside Jewish practice the soul of Judaism breathes which is a deep inner wisdom which is called kabbalah that translates directly to receiving.
Another way to translate it directly is to call it Torat ha-sod which means “secret teaching”. However it depends how you look at it, when saying it is secret teaching it is completely wrong as it actually means teaching of the secret. Many would say it is the same thing, however it is not secret teaching, but teaching of a deep secret. Not a secret that nobody should know and that there are something that needs to be hidden, but a teaching of something so deep and profound that it will open you up and reveal something hidden within you if you have a strong faith in Judaism.
Others who want to get technical could say that a taught secret is no longer a secret, however this is nothing artificial and nothing shrouded in secrecy, but a real secret that is integrated, analysed, illustrated and explained into a human consciousness. When you want to explain other secrets like those deep within us that we learn as children, live with daily and never learn to grasp in our daily lives but taking it for granted like the sheer magnitude of the magnitude and brilliance of the human brain.
This is how you could look at Kabbalah, it is a sense and a knowledge of the beyond, the understanding of what is impossible to understand. It is the danger as mystery cannot be held or wrapped up and the dangers of mysticism lies by a student trying to unravel the content. Teachers do not know if they are understood and his teachings could be misinterpreted and misunderstood and in essence lost on the student too.
Kabbalah has always been taught and transferred in confidence and only in recent years have progression been made to reveal the inners mysticisms and kabbalah openly while continuingly preserving the teaching’s purity. Another main reason is the misuse of this gift and people taking advantage that led to the believe of many other religions that Kabbalah is dark and evil only due to misuse.