While there is nothing crazy about the idea of giant primates in the past (there are fossil ones from China), the idea that they are running around in the USA is highly unlikely. With all the millions of Americans walking around with guns in the woods for centuries, no one has
ever shot one and recovered the body for examination. If they exist, that is just unbelievable. People have shot hundreds of thousands of bears, cougars, moose, elk, etc, but no one can shoot an 8 foot tall primate. That doesn't make any sense at all.
There is a significant amount of overlap between bigfoot sightings and black bear territory. I think a lot of the credible bigfoot sightings are black bears walking on two feet, as they do sometime. A black bear standing upright is about seven feet tall. Imagine a furry, seven foot tall creature walking upright in the bushes- what you going to think? Yeah, probably bigfoot. It is an easy mistake to make, I would imagine.
Here is a video of bears walking upright.
https://www.youtube.com/watch?v=U5cqbsCJ3gQ