Feraligatr, as any zoologist knows, are not bipeds but quadrupeds. It is true that their back legs are thicker than their front legs, that their prior forms of Totodile and Croconaw are bipedal, and that some pet Feraligatr can be trained to stand up, walk around a few steps, and use their newfound height to bite at flying-type prey. But any observation of them on land would reveal the need for four legs to have any sort of real mobility; a bipedal Feraligatr would struggle to so much as support its own weight for a prolonged period of time.
This misconception is enormously common, so much so that some editions of the pokedex devote space to debunking it, for it is an ancient artistic convention to depict Feraligatr standing up. The custom originated as a way to make the pokemon look more fearsome, and it has maintained itself through generations because it serves to anthropomorphize the pokemon. Famous paintings throughout the ages have portrayed Feraligatr in this way, whether they were receiving messages from Arceus or walking out of the ocean like the predecessors of man. Modern portrayals have tried harder to justify it, often showing them in battle or chomping at flying pokemon; few, however, have taken the step of showing them on all fours.
Most people will never encounter a Feraligatr on land. Wild Feraligatr are highly endangered and extremely dangerous, so people stay away from them. They are not considered a strong pokemon, and seldom seen in League events. Totodile are popular pets, but few pets train hard enough to evolve. And because of their enormous height, many zoos are reluctant to shell out the money for an expensive Feraligatr enclosure, for they average a height of 7'7'' when on all fours!
And so the myth survives.