I understand this view, but I always take it with a grain of salt, because when you look at the Monster Manual... that's just too many things.
Just to give a rough example,
@nevin mentions that the Polynesian people fish in shark infested waters. That is impressive, because we know that sharks are a dangerous threat.
But oceans in DnD have:
Giant Crabs
Merfolk
Tritons
Sea Elves
Giant Seahorses
Sharks
Giant Sharks
Sahuagin
Giant Octopus
Sea Spawn
Merrow
Plesiosaurus
Sea Hags
Deep Scions
Killer Whales
Kraken Priests
Water Elementals
Dragons
Sea Serpents
Dragon Turtles
Marid
Storm Giants
Krakens
Leviathans
And there used to be more, so you can pull from older editions as well for even more ocean or coastal threats. Now, obviously, it isn't going to be all of these things all of the time... but a lot of these things have large populations, and any of them could pose a major problem for a fishing village.
Now turn your gaze towards "forest monsters" or "surface cave-dwelling monsters" and these numbers swell. And, again obviously, a DM doesn't have to use all of these, but all of them do exist somewhere in most DnD worlds, and while in the real world something like a tiger can't really threaten a village or city too greatly... that's doesn't hold true for giants or a troll which could actually kill an entire village.