Never heard of it? Not surprised.
A great many of you know about currents and how wind affects the water. For instance, we know that the Gulf Stream exists because the wind blows the heated water from the tropics up north, where it cools at the arctic and travels down along the coast of Europe, back to Africa where the process starts over. This happens all over, including in the pacific ocean.
Now, this water may not be moving fast by a typical civilian standard, but it is moving. And when you have water moving in a vaguely circular pattern, the centripetal force will cause the center area to drop slightly as the edges rise. This creates a basin affect. In the pacific ocean, this basin has been collecting trash since people started tossing trash into the water. And remember, kids, plastic floats and lasts for centuries.