That charismatic chief was able to long foresee the fickleness of the merchants, which was why he attempted to prohibit trade between the two parties.
He did not want these leeches as he put them to interfere in the greater goals of the people for meager short term profit.
The leader even feared this trade was only a covert way for the enemy to infiltrate their ranks and so wanted to stop his infection right at the roots.
However that was easier said than done.
Because remember, to equip and maintain his army, he needed these merchants. The island natives were still unable to make their own weapons given their centuries of self isolation.
In fact, they could barely maintain them, with even small chips and cracks proving an immense challenge for them, whereas in the broader world, this tiny repair would have been a piece of cake for even a blacksmith's apprentice