Even if the will is free it is limited and restricted. It is as free as a prisoner in a prison cell. You can be free to some extent in your cell but only within that room. Determinism is the prison and the cage one is condemned to be "free" in. There are too many wires and cross connections between what one calls the self and the causal events that make up that self for there to be a clear free will.
Hume said reason is the slave of the passions one could say free will is the slave of determinism.