These concepts are work in progress materials and were not destined to be made public in the first place but still, we felt it would be nice to share them with the community.
One of our Concept Artists made these so 3D Artists then better know how to model the objects properly. For those among you not necesarily familiar with game development processes, it's fairly common you start working with concept art like these to give a "look and feel" and proportions of what the future in-game 3D props and world would look like.
It's a thing to picture it in your head, it's another to make it happen. You also need something that teamates can share and iterate on to make sure global vision is defined, known and understood by everybody.
Basically, these are some reasons why these concept arts exist and we hope you'll like them. Maybe you'll spot the 3D versions of these objects in-game someday and will remember their 2D concept counterparts. They could be very similar or quite different. That's also the nature of game development. Things are always in motion!