User blog comment:Garhdo/Why the Reapers attack Earth/@comment-2256917-20110212052854/@comment-70.208.129.227-20140527125310

during every cycle there are races that remain untouched by the reapers. they save the underdeveloped civilizations for the next cycle which is every 50,000 years instead of every 200,000 years. when the reapers began the first cycle they waited a lot longer than 50,000 years yo return because there was not enough to harvest