User blog comment:The Milkman/Mass Effect in Retrospect/@comment-4721065-20130419132524/@comment-24174486-20130419211612

"Why risk everything in one ship?"

Because they only have one ship that can go through the Omega-4 Relay. In that case, it makes sense to put all of their eggs in one basket, sending in the most talented and skilled people they can gather so that they have the best odds of accomplishing their mission. Sending "waves" through the Omega-4 Relay is simply not an option.