It's understandable until you consider that you live in the same food web as those fish, and ecosystems are a little more complex than "Divert all the top-level resources to humans".
It really comes down to living in a society with competing interests. Society has decided that protecting the last salmon is somewhat important. I say somewhat because central valley farmers are HEAVILY subsidized by the state and federal government and still to get to take the lions share of the water to grow water intensive crops on the desert heat.
What's that old saying? "When you are used to privilege, equality feels like oppression".