yeah, ilegal dumping is very frustrating, and something that sucks when you have land, as once someone does it, it's too late and it's very hard to stop. It's real bad when people have all ready loaded it up on a truck, all they have to do is drive to the dump, not the woods. Most places dumps and such are not even expensive.
I think where problems like yours pop up is when there are barriers, like places where getting construction dumpsters are insane prices. Or towns decide to ban having a dumpster in the driveway when someone is working on a house. Or the dumps/transfer stations have terrible hours, or don't let the public use them. It's something where barriers need to be set very low, remove reason doing anything but taking it to the dump. If people were dumping steel, then you know something is not working right there.
I think some folks, it just is something they grew up with, it's engrained, they just don't see the issue dumping it like what happened to you or they see it as their right, or how they always did it etc. Insane yes, but some people just do that sort of thing.