So? Exists = possible.
I doubt it. People are notoriously bad at estimating size of creatures observed in the wild. Put a coat of hair on someone Shaq-sized, have him stand on the side of a road to scare the bejeezus out of some unsuspecting passerby, and I bet the resulting description of our 7', 325 lb Shaq could easily be inflated to the 8', 400 or 500-lb variety bigfoot.
I've seen Shaq from about 30m away. His massiveness was obvious on sight.
Because it's all made up and/or misidentified. Plus, you've got to be careful not to cherry pick references to really huge bigfoots, because I've written several times already that those likely would be impossible.
Shaq is bigfoot-sized. The biomechanics of bipedalism in primates do not make bigfoot impossible, they only make outlandishly-large bigfoots impossible. Check out the infamous Fahrenbach footprint size distribution if you want to see a potential size distribution claimed for bigfoots.