But even if that’s true, why take the risk? How does putting up a weird monument in rural Georgia help them achieve their goals?

If I were in some shady global conspiracy with secret plots for population control, the last thing I would do would be to put up a bunch of coded references to my plans in public. It wouldn’t benefit me at all and it would increase my risks. It’d be like if the Mafia put up billboards confessing to their crimes in oblique riddles. That seems like Scooby Doo shit, not how actual criminal enterprises work.