Personal choice, the decision is that you give up distance for comfort. Lots of people opt to go ultralight, lots go heavy. It depends on a lot of things for each individual.
Everyone loses weight while hiking, my average 5 mile burn is about 1000 calories.
I would never carry a journal or anything paper other than a couple scraps of newspaper to help start a fire. But lots of hikers do carry a journal. I carry my cell, sometimes I'll carry a mini solar charger and I can text or play games if I'm bored. I carry a firearm for personal protection. Not many do. We can open carry while hiking here in FL, I usually carry concealed a small S&W 38 Airweight pistol. But if there are large game animals like bears, gators, panthers, I carry a larger firearm with more ammo, usually a Colt .45 pistol and several clips. And I open carry.
Little stuff adds up super fast. I like a nice tent, cooking options, towel and soap, etc. Extra 2-3 lbs right there. Aleve, Tums chewables, benadryl. Ear plugs. Carmex. Off, I never go on a hike without it. Sometimes water purification tabs. I'll take them to Nobles since there is a gator in the pond.
I'm also a foodie and bring fresh meat, usually steaks, for the first nights meal. Some potatoes, a couple small onions. Sometimes a bottle of WT101. Mini spice rack. Couple lbs there. For other days I like dried food like ramen noodles, I am a master at doctoring them up with canned chicken. Maybe some tuna pouches or some SPAM for another meal. Instant oatmeal. I'm a coffee fanatic, my kitchen looks like a Starbucks but I carry instant coffee on the trail. As heavy as I go the weight of a French press isn't worth it. Anyway food bag is usually 4-5lbs.
Water is 2.2lbs per liter. He was probably carrying 3l when he broke camp. 6.6 lbs.
Like I said most thru hikers have somebody stashing supplies for them. A wife or GF or mom to Fedex stuff back and get new gear.