Except only 'fall' can correctly be applied to a single waterfall, while 'falls' requires a series or group of some sort. In practice it's a pretty soft requirement since places like Niagara Falls can be considered several falls adjacent to each other, so it may seem to be breaking (and thereby devaluing) the rule in plain sight, but it's not. Or in Yosemite, visitors complain when they're corrected to say "Vernal Fall" and "Nevada Fall", instead of Falls for each of those, and they point to Yosemite Falls as a counterexample. But the thing is, Yosemite Falls is actually a series of three distinct and separated waterfalls.
Ultimately, though, it's another of those places where people know the rules but it's just not that important to follow the rules. I am only mentioning it here for the reason that when we're in language learning and translation mode, rules matter a little more, then we can break them all day long after that.