Even before the multi rotors were available, the various manufacturers started producing the "Park Flyer" lineup with easy to fly and small aircraft that encouraged
the end users to fly anywhere but an AMA club field. Now take the group of folks that embraced that idea and give them an instant gratification toy such as the multirotors and it's all downhill from there. No skills learned, no education in aerodynamics, nothing but launching a toy that can be a safety problem to people and property with no education of either.
I know that the park flyers can and have been used in a safe manner at fields other than sanctioned AMA sites, But not all the users of such things take the time to consider whether or not the site they are using is appropriate for such use.