Because I think that some things, and fish are among them, ought to be free to anyone. It drives me crazy that to through a piece of bait on a hook and catch a trout I have to pay a license to my state. It's fish. God made them. Nobody ought to own them. Someone may own the PROPERTY on which they swim and I ought to get permission from the owner to catch them, but the fish themselves ought to be available. In the case of international waters, I do not think we ought to have someone "own" those grounds. They ought to be available to anyone with a boat, a net and the guts to go catch them. Wise management says that the users ought to agree on some sensible rules, but nobody ought to be able to force someone to go home after they've caught half a boatload. On national fishing grounds, yes the nation can manage it anyway it wants - and probably should for reasons you have pointed out. But international waters ought to be free.
While I can see what you're saying here Pooch, I should add that these resources, held in common, should also be managed. The fee (for your fishing license, for a commercial fisherman's license, etc.) is ostensibly to pay for that management. It doesn't always work that way, but that's the justification, and in my mind, that's fair. Personally, I see it as cost effective: I can plop down $45 for a combination license here, that lets me fish in salt and freshwater, and harvest shellfish. Take that $45, add another $150 for bait, gas, tackle, etc, and I can go out three weekends in the summer, catch 8 coho salmon averaging 10lbs apiece. That's 80 pounds of fish that sells for upwards of $9 a pound in the grocery store, for a total cost of $720. That (to me) is well worth the price of the license that pays to sustain the fishery.
I understand also what Prince is saying, regarding the long term vs. short term dividends for the user/harvester of the resource. But to me, that's an idealized outlook. Several species have been pushed to the brink of non sustainability through commercial harvesting. The best advice and argument that I can offer as a refutation to your scenario Prince, is to read the book "Collapse" by Jared Diamond. In the book, he articulately demonstrates that throughout human history, several human societies have doomed themselves through short sighted thinking, from the Anasazi in the American SW to the Norse colonists on Greenland.
A third issue regarding fish stock management, is that several species are migratory. Salmon, for example, migrate throughout the Pacific, especially the north Pacific, before returning to their home stream to spawn. In effect, you have to have several branches of management: from spawn until the fish returns to the ocean (this would be the management of the home stream) the migration and life cycle in the open ocean (and all nations who are able to harvest, this leads to potentially numerous sub management branches) and the return of the fish to the home stream for the spawn. Any management style that refuses to take any or all of these factors into consideration is doomed to fail. With numerous species holding at 10% or less of former stocks, this is an issue of global importance to the consumer, the harvester, and the manager.