Actually, if you think about it, the creation of memory orbs makes perfect sense. As you note, most of the orbs involve secret dealings and other dirty laundry that the makers probably wouldn't want anyone finding out about…and then remember that for all the technology, the FoE world is still a land of MAGIC that includes various means of reading minds and memories. Then recall that by making a memory orb, the person loses those memories, removing them from from their mind and, thus ensuring that if they were brainscanned, those secrets wouldn't fall into the hands of whoever was doing the scanning.You might ask why not just destroy the orbs after they're made then? The answer is the same reason for their creation: they contain classified information, information that they took out of their minds to protect, but that they also might need to know again at some point, hence why the orbs weren't just smashed after creation.In addition, a good portion of memory orbs contain personal memories from their creator's pasts, memories that they'd want to keep preserved either for themselves or to share with their loved ones.As to how these memory orbs get scattered all over, well add 200+ years since their creation and mix in dozens of scavengers and looters finding and trading them to interested parties, and it's not too inconceivable that over the time since the bombs fell and the start of the stories, all but the most secured orbs have gotten pretty spread around.