Who didn't want slavery to end?

Slaveowners, and those who were strong supporters of states' rights. While many white Southerners did not own slaves, those who did often owned dozens or hundreds of them. If slavery was ended then they wouldn't be able to profit as much for their land and become wealthier. Slavery was an essential part of the economy in the Southern United States.

Some people supported the right to own slaves not because they owned slaves personally, but because they were strongly dedicated to states' rights. Because slavery was not mentioned during the writing of the Constitution, it was assumed that it could continue to exist, and could only be regulated by individual states. Those who argued for a federal ban of slavery were considered to be infringing on the rights of states to decide things or their citizens when the power was not explicitly given to the national government.

Additionally, many people in the United States were not actively for or against slavery, but utterly neutral.