The Northern did want Missouri to become a statehood as a slave state because they want more free territory. The Northern senators want to outlaw slavery completely to get more territory.
The Missouri Compromise was made to the nation more politically. It was also made to keep slavery from being the "deciding factor" in final discussions.
The Southerners did not want Missouri to be a statehood as a slave slate. The Southerners would end up not having as many slaves and they love having slaves. The slaves do mostly all the work for them.