The North Pacific Gyre is the size of Africa. …
The North Pacific Gyre is the size of Africa and it has been estimated to contain six times less wildlife than plastic debris.
As it weathers it breaks up into small pieces which weather into smaller pieces. Also with the larger surface area and excoriated surfaces, they can absorb organic chemicals far better than most other objects found floating in the sea.
Organic solutions present from urban drains and farming run-off cling to the small floating debris and both seem to be absorbed by plankton feeders.
Stuff the size of cutlery and cigarette lighters can be mistaken for fish and preyed upon by seabirds -among other hunters. The rest, presumably, washes ashore for a while before going around the gyre once again.
The result is an annual increase that is not likely to cease until the sea is so deeply covered that plastic blots out so much sunlight that photosynthesis can not take place.
Not that things will alter much by then as creatures of the upper food chains will be extinct.