It's likely because you don't see a lot of non-infantry uniformed military sporting expedition grade packs. These tac-packs were carry over from war, which we've been exposed to continuously now for over a decade. Like I said, we had these as go bags in Baghdad in 2005; every mainline contractor seemed to have something like this over there. I kept mine hanging on the wall beside my body armor next to my door, or at the end of my cot facing the tent opening. When the whistle blew, you slid on your boots and your helmet, grabbed your bag and your armor, and ran for the bunker. If you had to be evaced, you had the basics you needed with you; the rest you left for later, assuming you could get back. Since then I've augmented the pack, and yes, it is awkward compared to my external frame hunting/hiking pack. If I were planning on going cross country, I would grab the framed pack. But for day to day stuff, the Motherlode is adequate.

Funny, except for the self defense/E&E stuff, my loadout for the big pack for bug out (or whatever) is strikingly similar to what I'd take for a two week hiking trip for recreation.