They are representation of some resources to be gathered. Yes, they look like some super cool future containers, but it is just visible representation of resources available in the surroundings. You can cosider them as blueprints, advanced pieces of equipment, tools, planks, food cans, vehicle parts etc.
Left by other humans. They can be considered to be some storages like footlockers, old boxes, safes, holes in the ground covered by some planks. But that would need a lot of new graphic objects and some algorithms to fit them into surroundings. This design was left as is right now to save time for other elements of the game.
Because people left them there not taken when killed or evacuated.
To prevent you from taking them.
Maybe later Snapshot will upgrade them. But who knows. This is really low priority problem for me. When SG won’t have much to do (fix PP1 or make a sequel) they can work on additional props to replace the old ones. 