Curiosity.
Odysseus is a self-assured guy who lives by his courage as well as his wiles. He's an intellectual; and although he is self-disciplined, his curiosity sometimes gets him into a lot of trouble. Odysseus is also willing to pay a price for knowledge. It is this intellectual curiosity that drives him to hear the Sirens' song despite the pain he must endure while being tied up to the mast of his ship. If it weren't for those excruciating straps, he would have been lured to his death.
So what was so enticing about the Sirens' song? They promised gifts of wisdom and knowledge of the future. Who could resist that?
Hope this helped! :)