Scouting. They traded a first round pick for Favre. In Favre's one season in Atlanta he threw four passes, had zero completions, and two interceptions. To trade a first round pick for that means their scouts clearly knew something no one else did.
Brian Gutekunst is their current GM, he was not around when they traded for Favre, but he was a scout when they drafted Rodgers and as GM drafted Love.
They just seem to have "it" for finding their QBs of the last three decades and potentially another ten to fifteen years.