If it was rainy, as Swanny said, that would explain why none appeared for a while.
I was kind of kidding about Monsanto, though some crop circles, I've heard (e.g. on THEWATCHER's thread) are not created by ETs - the tech is also used by the military etc. BUT, if it is a beautiful imprint from off-world intelligence, on a grouped species, theoretically, as humans who view them, they are meant for us, as a grouped species.
Humans are genetically similar like crops.
Or
They're not meant for us, at all (though we get to notice!). Earth is a way station. It's a communication . Maybe
between ETs. Or maybe an ancient us - who kind of forgets WTF it is we're supposed to recognize.