Cultivators had become something of an open secret in the present day.
Those in the know had begun to practice whatever cultivation method that they could get their hands on. Few if any of them felt inclined to draw attention to what they managed to gain because they were all motivated by selfish intentions.
Human society was very much hierarchical and based on competition. Only a small proportion of people had a chance of occupying the positions at the top.
The more competent and capable they became, the greater the chance they could climb up the ladder.
It became a lot harder to defeat the competition if their rivals started to practice the same cultivation methods that made them smarter or better at their jobs.
This was why the earliest wave of human cultivators all abided by an unspoken rule. Every beneficiary implicitly colluded with each other to prevent the general public from learning about the wonders of cultivation.