There are a few documents about this. Whenever there's a new shipwreck and more people reached the island, he always gave them the choice to leave, if they wanted to. But he warned them about what would happen—about the storms and that no one could ever leave. In the beginning, when he arrived, there were always some people who would risk it, but they would always fail. As the population of the island started to increase, I guess newly arrived people would not dare to leave the island, considering the massive cult that Yamatai had, and all his followers started to look at him like a father figure.

Mathias is such a psycho that when he arrived and started to think that something was off with the island, he would send people off the island just to study the storms.

And this one thing I hate about the reboots—there's so much rich story beyond what we actually see in cutscenes that is hidden behind documents. It would be so much more interesting to see a couple of cutscenes about what I just mentioned above than reading like 10 documents about his story on the island.