Didn’t they fall for the climate crisis of their time and stopped fishing then turned to cannibalism then vanished ?
I was watching something on PBS about Easter Island, just the other day. A couple of archeologists surveyed and carbon-14 dated fire pits throughout the island. What they concluded was that the population was stable at around 2000 people from the 13th century (it was settled from other Polynesian islands around 1210) until the arrival of Europeans. The problem with Europeans was they brought with them diseases that Polynesians had not developed immunity to, not warfare, slavery or anything deliberate.
There is an island off the coast of India to which travel by outsiders is prohibited because its stone age isolated population almost certainly has no immunity to modern diseases.