Why does some sexual relations in the Bible lead to death and others being cut off?

Reading Leviticus 20. I feel as though God is having to train the Israelites to be good and holy. It’s not a duh to them to not sleep with their sister or mother or whatever. So he’s laying out all the details and being exact. But why do some sexual relationships lead to death while others only being cut off from their people? I know not all of God’s commands have an obvious why He made it that way but does anyone know? TIA