Because popular sovereignty was well supported because it allowed the local citizens of a territory to decide if slavery was to be allowed or illegal. Stephen A. Douglas pushed for popular sovereignty during the 1840's.
Popular sovereignty is a political principle that is very present in the politics of the United States. This principle states that the authority of a state comes from the consent of its people through their elected representatives. In practical terms, this means that citizens are the ones who hold all power of the state and who can make decisions.
Popular sovereignty was considered a just and fair way to settle the slavery question, because this gave each state the right to decide whether to practice slavery or not. It was believed that by giving the states this right, the will of the people was respected.
Is there more to this, well sure, because I give my effort to help people and communicate with them if I am not 100 sure, so you can trust me not to just say random stuff
