Obedience to authority . The first person to speak gets the advantage of setting the stage. The person who follows must break down the arguments and scenario as presented by the first speaker, while also presenting their own perspective. While the last word is certainly beneficial, being first provides a decided advantage. This is apparent to anyone who ever had a group project in school or at work in which peoples' individual effort could not be determined by the teacher or boss.
Someone ends up with the lion's share of the work, and an equal share in the payoff.
Groups will generally make more moderate decisions than a single individual will. Groups actually will make more extreme decisions than will individuals. This is a polarization of groups into more extreme opinions and plans. While a bit of variation makes for interest, opposites are generally rejected and we search for people much like ourselves. As with this cliche, there are often counter-cliches that say the reverse, but are also believed to be true.