Yeah, but I guess it comes down to two different perspectives on the whole Bigfoot thing. On one side, we have the people who believe Bigfoot is a real animal, some kind of primate or primitive human actually living in the forest. And on the other side, we have the people who believe it's some kind of interdimensional entity, perhaps a space alien or, why not, a demon of the forest.
It's easy to dismiss the first hypothesis based on the logic you've presented. Obviously, a breeding population would leave some sort of evidence behind. And I guess that's why the second type of claim has emerged among believers in the paranormal. All arguments about the lack of traces left behind by this large-footed primate in the forest can immediately be dismissed, since an interdimensional being "wouldn't leave such traces behind."