That’s a great mystery to me too, Jake, as I have never heard of a boot rated to carry 30 pounds (plus hiker, of course), or 50, or 70, or 200 for that matter. Boots typically are rated according to their intended useday hiking on good trails, off-trail hiking, short backpacking trips, extended backpacking, mountaineering, etc. Of course, there’s also the assumption that a day hiker will carry less than a weeklong backpacker. And no allowance is made for the weight of the hikersomeone who weighs 250 pounds should, in my view, always be wearing a beefier boot than someone who weighs 150 pounds. To some extent a particular boot model will become inherently heavier as it is scaled up in size, but the materials used in a size five boot and a size 13 are the same, so there’s not too much benefit there.
My own belief is that most hikers are under-booted. That is, they’re hiking in footwear lighter than they need. Good boots are incredibly important; your feet take a pounding when hiking, and decent ankle and arch support is vital. In my opinion, manufacturers tend to rate their boots a notch too low. Most of the time a boot rated as a “light backpacking boot” is more like a decent day hiker if you’re carrying any kind of a pack and hiking on moderately rough terrain. I concede there’s a tradeoff as weight on your feet increases the fatigue factor. But I generally think people ought to get a slightly heavier boot than perhaps would be advised given a manufacturer’s specification and the wearer’s hiking habits.