Conceptually, military packs are built to take over-sized or overweight loads (mortar rounds, radios, etc.) and stand up to being tossed off an LMTV by an angry 18-year old repeatedly. That same design also has to live up to being tied on to someone that jumps out of a marginally-intact aircraft. It also has to work in the Iraqi desert, Arctic tundra, and deep jungle. Finally, they're ordering 1.2 million of them in five to ten year increments with miles or red tape and federal acquisition authority rules and regulations.
Compromises were made.