Bigfoot did it.
I remember a Dilbert comic strip from years back where Dogbert sums it up nicely.
His comment was along the lines of “Do we want to communicate with aliens who communicate by stomping on wheat?”
Seems very likely: it’s hopped-up wallabies in Tasmania, apparently.
Holy crap, I don’t think I’ve ever seen a more lopsided poll! :eek:
Seems fairly obvious that most of them are created by UFOs.
Unidentified Flattening Objects.
Oops. Voted for “don’t know, probably rational explanation” but meant to vote for “people did it, they’re just screwing with us”.
It looks like you have found the answer 
Looks like “they” took exception to the OP blowing the lid off this thing.
Sorry, Sworn to secrecy.
I don’t know why this is still in doubt. The originators have come forward; they and others have shown a variety of methods (it ain’t difficult). Hell, they have annual contests.
It’s depressing that, apart from accidental mis-votes, the poll isn’t 100% “people did it to screw with us.”
I don’t know why. A perfectly normal and healthy propensity for humour would produce a few outlier votes, even if the poll didn’t explicitly invite them.
Besides which, “Don’t know, but there’s probably a rational (non-alien) explanation” (the second-highest ranking option) seems like a perfectly reasonable statement from someone who doesn’t know much about the subject, or has read conflicting and/or inaccurate information about it.
Unfortunately, they only 'fessed up after other people had spent a decade or more investing a good deal of time and belief into a variety of alternative explanations (of varying levels of woo). With the result that they were decried as mere hoaxers and energetically “debunked” by the bunko artists, who claimed to be able to detect the difference between a man-made crop circle and a “real” one. Of course they couldn’t, but by the time that was proven the waters had been muddied enough for anyone not paying much attention to miss it.
Why isn’t there an option for “viral marketing campaign for Signs”?
Aliens made them and they are warning us to become a 100% Christian planet or else they are going to destroy us. Well non-chrsitians, are you going to convert to the good word or destroy us all due to your selfishness?
That made me giggle.
But seriously, it’s obvious that people under 30 are at fault. 
That would fall under humans messing with us. I mean, have you seen Signs?
Look here http://www.circlemakers.org/ for plenty on UK crop circles by the guys who made them. No aliens about.