Biblical covenants arose, even though initiated by God, out of sinful mankind’s ignorance of God and our experience of broken life due to our distance from God because of sin. God does not need a framework guaranteeing what his action or relationship with us will be; mere humans, uncertain and mystified, find it helpful.
God knows his own mind and it does not and will not change (which, BTW, thoroughly blows supersessionism out of the water). Nothing innate in him requires a contract to hold him to his promises, good faith, and integrity. Sin and separation has left us dark as to what might be in his heart, and his judgments have proven frightening: covenants are his attempt to help us understand his reliability while we are in our desperate fallibility. All he asks of us is faith, we ask him to put that in writing.
In placing the onus for covenants within the nature of God, it seems to me that Covenantalism reduces God to the level of sinful humanity; i.e. that he has to have a contract to be trusted. We cannot be trusted whether or not we have one, but once a person has been born of the Spirit, rewritten in heart as it were, the concept of covenant is superfluous. That person is one with Christ, sharing the life of Christ and having the mind of Christ, where is the need for an arm's length contract?
Covenants were nothing more than a teaching device for mere humanity that was necessary until the regeneration of the Holy Spirit was possible. That required penal substitution and identification to be established in time. So, though I understand the validity of covenant in bringing sinful mankind into contact with God, I see that Christ is not really offering us a new contract with God--he's offering us a new existence in synergy with God, which is why covenantalism falls short.