There's a difference between science has not identified a bunch of animals and science has not identified a 6-8 foot ape like creature in the north american woodlands. We have a really good idea where to look for bigfoot, we have no idea where to look for "unknown species #1" because we simply don't have a description of what we are looking for or where we need to look for it.

The difference is largely like asking "do you think you have an uncle Jim who is around 6 ft tall and has blonde hair who lives in Canada?" vs. "have you seen ever person in the continental US?". The answer to the first one is pretty easy to be sure of, check birth records from your grandparents, see if there's photo's of him, unless someone is hiding him you will find him or solid evidence. In the other situation it's just so massive that there's a guarantee that you will miss something you just don't know where to start looking unless you canvased every square inch of the US.

So with all the knowledge of the size, shape and location of Bigfoot do you really think it's possible that a community of these things could remain hidden? We know what and where to look for Bigfoot and have a ton of technology to find them, it's highly unlikely they would have stayed hidden.