How do we even know this is the Earth they were searching for. All we know is Starbuck got a signal in a revamped Viper that lead the fleet to this planet. They assumed it was the earth in their sacred texts. Did the constellations match what Adama and friends saw in that season 1 or 2 episode? It was never mentioned. Its BSG, who knows what the hell is going on
Actually the Constellations did match.