There are a lot of reasons that ships are not tracked.
In the particular cases of fishing vessels, even if they are registered and fishing legally in designated waters, they are still in competition with other legal vessels doing the same thing. So, if they think that they have specific knowledge of a "hot spot" to make a big catch, they are usually interested in getting there and doing their fishing without anybody else knowing where they are catching so many fish. Turning off their AIS is just "normal" behavior.
Add to that the rich who don't want to be tracked, the ships dodging all the "sanctions" imposed on various international trades, naval vessels that don't want to be tracked by "the other guys" and the actual pirates, it is no wonder that 75% of the ship traffic is not on the tracking channels.
So, I think this satellite visual tracking capability is a good way to get a handle on not only how much of some activities are occurring, but also who is doing them. It might sound like "Big Brother in the Sky", but it is also like "The Wild West" on the water at this point.