Throw a line in the pond, whatever bites will bite. Clean it and you've got dinner.
Versus with hunting, historically (and even now) if you miss your shot or don't hit a part that immediately takes it down, now you've got an angry wolf/bear/moose bearing down on you. Wolf is also probably too close to dog for most cultures.
Nowadays you can get meat from bear/moose/whatever, but there isn't much of a culinary tradition associated with them. So the only people out for them are the curious or macho types
On top of that, you can't really farm predators, almost by definition (I'm sure you could but that would be very stupid).
The most common fish that we eat are those that other fish also eat, like herring, and there aren't a good comparable land based animal in our current diet. It would be a bit like if a primary diet for humans would be wild rodents.
One reason could be that fish like herring schools, but wild rodents don't. It is easier to hunt large quantity of animals if they are located in the same location and bunched up.
I've never had the chance to eat cougar, but I've talked to folks who have, and they say it's their favorite meat - like a light, tender pork.
That's surprising. I would've thought it'd be dry. Or even fishy.