Finding new larger animals is pretty rare - from what I know. Most of the species being found are very small, and as you get bigger you get further and further into remote regions on continents with jungles on them - which we don't have. Also, there aren't any other known primates native to North America, which would make finding giant apes here very unusual.
But this exactly explains what I'm saying. Before science we'd go on our observations to understand the world - and science is about understanding things beyond personal observation.Northeast Ohio where I live is crawling with bears, but in 40 years I've never seen one. Does that mean bears don't exist?