The I know a few of these folks and they do 30+ miles a day on the CT and PT trails. You can't do that with a 50+lb day after day.
The other thing I find is that when most of us go camping we want all the comforts of home, look at RVers, UGH. One complainto of European climbers have of American climber is that US climbes sone want to be cold so carry much heavier equipment, same for BPers.
What Ultralight BPing does is to challenge the paradim that most folks have.
cheers