Slavery mainly existed in the Southern colonies but not in the New England colonies because the South relied on slave labor to tend to plantations, as this was their main source of income.
The South had a hotter climate, which was perfect for growing crops. This also meant the soil was better as well. The Northern colonies had colder weather and their soil was not very suitable for constant farming.
This meant that the South relied on agriculture for their income, they would grow and sell cash crops such as cotton and tobacco overseas. They had little industries and were mainly rural. The North had industries and that was their main source of income.