>why countries are letting those small, insignificant islands and countries manage all this wealth

Enlightened self interest. Those "insignificant" islands are generally speaking countries. By showing respect for the rule of law even in situations where they could easily overwhelm with force or economic power smaller nations, the larger ones reinforce that the law matters.

The larger countries use as a defense the idea that something is an "internal matter", IE it's no one else's business. If they bully their way into other smaller countries' business, then they open themselves up to the same interference.

Might does not make one right. Law does.