Two reasons: One, Jor-El was the biggest advocate for the doomsday theory, only he was also about half as looney as Zod. Jor-El felt there was no point in saving anyone on Krypton, only in insuring the future of the Krypton race. And Two: Once Jor-El was dead, there was no longer anyone to ring the alarm bell anyway, and the Council was never convinced of Jor-El's doomsaying.
Also: You guys didn't like the score?! That was the only thing I thought they got 100% right.