Board Thread:Show-Related Questions/@comment-45.16.198.184-20150626221131/@comment-26247132-20150626224745

To prevent spoiling anything for you, what episode are you on?

A somewhat non-spoilery answer is that they had enough drop ships for 700 people but there were well over 2000 people on the Ark. The 100 were expendable so they were the first to be sent (giving the Ark an extra month of oxygen) to see if earth was survivable. To send another 209 down would be wasting drop ships for the future generations if earth turned out to not be survivable at that time.