For anyone even mildly interested in crime, exploitation, vigilantes and other human stories across the oceans, check out The Outlaw Ocean by NYT journalist Ian Urbina. Brilliant work.
I'm in the middle of it right now! In addition to some amazing first-person narrative about life at sea, it does answer a lot of the "why don't they just" questions in this thread. However he doesn't offer a solution to the fundamental tragedy of the commons problem. As with many other global problems, there seems no way to solve this without global government co-ordination, which seems pretty unlikely.
https://www.goodreads.com/book/show/43345615-the-outlaw-ocea...