What restricted regions represented was a zone which possessed thicker concentrations of dimension energy and was a place where a large number of mutated lifeforms would frequently gather. The evolution index within was very high and completely surpassed that of any ordinary wilderness area. Along with this, the changes to the environment was very severe as the terrain and climate became complex.
The army itself had difficulty suppressing such regions and could only explore, observe, and record what they could. At appropriate times they would send out troops to clean them up.
Naturally, quite a number of homeless mercenaries and refugees chose to hunt and kill a few low ranked mutated beasts in the less dangerous restricted regions. They would use up the corpse and harvest the crystals for those who needed them in exchange for various resources.