desensitization?
Could be, or just "system overload," or just kids using available tools in more sophisticated and clever ways.
See Series of robo-call bomb threats sent out to schools across state - The Boston Globe - April 11, 2016
Ed Davis, the former Boston police commissioner, believes the threats could be coming from abroad. He said the perpetrators use computer programs that allow them to disguise their location, making them difficult to track. ...Threats that targeted Rhode Island schools earlier this year probably came from Russia, authorities said.