Technically, the orb is an image of the lens aperture; this is the reason it has sharp edges and often has a structured interior (a picture of nearly invisible dirt on the lens). It comes because a nearly point shaped light-source (usually the flash reflected from a dust particle, raindrop, etc.) in the image area. It does not even have to be out of focus, a point light-source may project an image of the lens at all focus lengths.
You can watch an orb without a camara: Take a small round shiny object. A steel ball is excellent, but a knee of a paper clip will do. Put it close to your eye, in a clear light. It is best if you can avoid the light shining directly into your eye, do it at the rim of a lampshade, or let sunlight strike the object from the side.
You will see the light in the object as an orb. Squint or blink your eye, and you see the orb flatten as your eyelids come down. You will also be able to see the fluid on your eyeball as you blink, and sometimes your eyelashes.
Some camaras make hexagonal orbs, because their lens aperture is hexagonal.
So, why do people want to think they are anything else? Simply because some people want desperately to believe.
As Randi says, believers are liars; they lie to themselves.
Hans