I strength train for a bunch of numerous reasons. Mental health, mental toughness, and performance. I've found I'm mentally in a much better place and have found direct correlation to my back country performance. My simpleton brain is like this: Heavy pack + strong body = lighter pack weight...
The phrase, "Ounces equal pounds, pounds equal pain" resounds with me. While I don't go absolutely nuts with it, I can definitely notice a difference over a long period of time FWIW.