You may as well ask why the planet has spawned and extinguished the myriad hominids and hominoid species it has over the eons. "Because it can" would be the only suitable statement you can really make about any such natural occurrence.
I've always loved this quote attributed usually to the naturalist J.B.S. Haldane (possibly an apocryphal quote, but still accurate) after being asked what he had deduced about [Mother Nature] after a lifetime of studying insects: "[She] has an inordinate fondness for beetles", he said. This is just another way of saying, "Because a beetle fits more biologic niches than any other taxonomically similar organisms, it exists in greater numbers"
I have always viewed the non-existence of Sasquatch as much, much more improbable than existence....and you could toss all the sighting reports/ photos/films/tracks and be on sound scientific ground with that conclusion. Wherever you look on this planet, if you are able to define a niche that life CAN exploit, it WILL be there. The niche for Sasquatch has been pretty well defined at this point. The confirmation part is just mopping-up to satisfy those who aren't paying that close attention.