They're intended to protect from the elements as well as from monsters. Thus all the extra materials and excessive wads of duct tape on top of the bags and body armor. Basically it's so high-end survivors that don't want power armor have a nice alternative in the form of different armored suits.
I can include the requirement for a rain coat in there as well.

Think this:  http://fc00.deviantart.net/fs71/f/2010/203/9/1/I_ran_out_of_STALKER_phrases_by_flyingdebris.jpg