The Isrealites were choosingto forsake the relationship established through the Old Covenant. Why? Because they had a defiant and a rebellious heart! "Revolting" and "departing" indicates a conscious choosing.
How is this fault going to be overcome? By changing the nature of the party making the New Covenant, so that the flaw is removed. In Hebrews 8:10, Paul says that the reason for making the New Covenant is so God's law can be written in the heart.