Not saying you need it for 'em, but have you noted the size of some black bears found
in PA. - upwards of 500-600lbs. Then there's griz in Idaho, Montana & Wyoming.
Of course, encounters are rare, and in most cases all you have to do is slowly back away. Making a little noise (whistling, etc.) as you walk along will generally keep you out of any trouble in the first place. Most cases, carrying some pepper spray will do the job. But, Lord help you if you stumble upon a sow with her cubs, and she sees you as a threat. Or, you get too close to a food cache at the wrong time, or just happen to startle one who's having a bad day, and decides to make it better - at your expense.
And, of course, it can be just plain "comforting" to have the gun along - just in case.