system
A chat on 4chan
human
think of it like poker. you are just learning the rules of the game. you may not fully understand the value of your own hand. A more advanced player may be thinking about what you have, an even more advanced player what you think they have, etc. 

Now imagine me talking about a 4-bet or something else very advanced. You would not understand. And if you would, then there is still no need to tell you: you are practically bleeding money. 

The exact fact that you can not see clearly allows occultists to move you in line with their will. Why raise the blindfold?

But that is about selfish power. There is also a reason to keep things hidden, not about power gain and control: people do not understand and fear the occult. they do not even fully understand their own sexuality, so how would they view sex magick with a pantheon of sexual identities? Also, some occult knowledge can be very powerful and dangerous in the wrong hands. It is bad practice to introduce someone to arcane knowledge when they are not ready. They could go power hungry or insane.
gpt
more directly: knowledge is power. knowledge has value. share the magic trick or weapon blueprint with the world, and you lose your advantage.

Lastly, there is something very alluring to arcane hidden knowledge and feeling like you are 'in the know and special'. Many cults use this to trap you. People joining a secret organization expect to be privvy to secret knowledge. This is almost primal: only you knowing of the location of a food source gives you a lot of power and potential calories to use for mating. Arcane knowledge, like big boobies, makes your mind drool. If you do not have real arcane knowledge, just make something up and do not tell anyone but new recruits. You just made something of value out of nothing.
human
Like genes are passed down from generations of royalty to their generations, so does arcane knowledge get passed down. Some knowledge is meant for your spawn or kin or peers, it is what makes you a powerful family. If such knowledge is meant for you, it will be open and taught from when you are little. If such knowledge is not meant for you it will look like a closed puzzle box. You require other pieces of knowledge and experience as a key to open up the box and begin your investigation. This is all by design. It is a real knowledge economy, much like early mathematicians and alchemists kept their recipes a secret or used these to trade for other approaches. In books, you repay with gold. In communities you pay with your own knowledge.
gpt
you can not learn to hack from a book. Hackers do not write books for beginners. you learn by doing. then when you are ready to join a group, you have to search in spots where normies do not know to go. to enter the group, you usually have to provide an original exploit or hack, that you wrote yourself. only then you get access to the box of exploits and ideas from the group. you are always more powerful as a group, but also more vulnerable. someone could expose the inner secrets or rat you out to the police/inquisition.

and it would be a terrible idea to share these loopholes and exploits with the wider public. if they are not ready, they will misuse and attack innocents. or overdo it and end up babbling in a jail cell. you would also draw attention to your group. is that all you released or do you have even more?

just not a good idea for elite /advanced initiates to work together, without keeping knowledge occult. drug gangs and cults usually keep naked photos or blackmail to ensure your silence. this only increases the impressive ritualistic power of arcane knowledge. now it is actually dangerous to know about.