This is to reply to your edit.
Certainly I could understand the scenario you laid out as happening a lot of the time. On the other hand, I'm just not confident in saying absolutely 100% of all supposed bigfoot sightings are fake or mis-identified black bears. Even if most bigfoot reports fall under this category, that still leaves a certain percentage that is unexplained. Certainly, the kind of people who grew up and/or hunt and camp in the woods are very aware of tracking certain animals, etc., and know what black bears look like. They seem to be pretty adamant of what they saw, and often the description is quite a bit different that what a bear looks and acts like. Some even have video and audio of the vocalizations which anyone can run through a spectrum analyzer and come to the same conclusions that humans cannot produce those particular frequencies. Could they be put ons, or fakes, sure, but again, I just have a difficult time committing to an absolute and saying 100% are fake.
I don't know what it is, but something is happening to either cause people to collectively hallucinate (in corroborated reports of more than 1 person), or it's some kind of collective unconscious archetype (Jung). Maybe densely packed forests have some kind of endogenous psychedelic that we don't know about and that is what is causing the phenomena - I just don't know.