Because that is how nature works. If your dumber, slower, weaker than another species competing for your resources?
You loose.
Modern humans are the ultimate survivors in a battle royal hominid cage match going back a hundred thousand years.
If Sasquatch is a competing hominid? Then it's fate would have been decided in the same cage match. With it either losing to or displacing us.
Of course the other option is is that it's not a competing hominid and instead just a bipedal ape with no understanding or need of fire, shelter, stone tools, etc. therefore they simply stay at the corner of mans world and eat the bread crumbs left behind by humans.
But make no mistake if they were humans too? They would not be content with this arrangement.