the influence of the ring is so powerful that no one, not even frodo, would have been able to willingly throw it away. Frodo's ability to withstand the ring's influence for so long is already a testament to his willpower. And his compassion for gollum is what ultimately allows the ring to be destroyed; he shows pity for gollum and spares his life, and gollum's intervention is what unintentionally destroys the ring (the only way it could be destroyed).