In "Cold Medalists", the twins are horrified at the prospect of Nod's Limbs being destroyed, even though they hate everyone in it. No other place has people who are dumb enough to fall for the twins' scams.
Some of Edgar and Ellen's plans could cause mass destruction and serious harm to the victims. These pranks were only stopped because circumstances prevented them from being able to pull them off.
Edgar and Ellen's money making schemes often fail, which seems like Laser-Guided Karma until you realize that they're orphans who probably don't have any other way to get money.