Why do you suppose it was necessary, as part of the Missouri Compromise, to allow both Maine and Missouri to become states at the same time? It saved Congress money and time; by admitting two states under a single bill the process was less expensive and required less debate.

It allowed Maine, which was much smaller, to have all of the rights and privileges of Missouri without taxing its existing structure.

It maintained a balance of power between the Southern tier of states that legally practiced slavery and those in the North that prohibited the practice.

It allowed the United States to gain strategic coastal land (Maine) and natural resources (Missouri) for the common defense against foreign invasion.