Hell, man, it takes little more than a well-organized team of lawn mowers carrying GPS receivers with waypoints programmed in. Same method as corn mazes.
As for "world-wide," we've got a fine example of how people from all over get together and plan and discuss things right here at FR. And gaming communities are far more organized than we are. It's easy to predict that there's a "crop circle" community out there somewhere.
Little green men from Mars is a less absurd explanation than that.
Your assertion is simply NOT TRUE.
Your post makes it sound like you know virtually nothing factual about the phenomenon.