It's the same thing that drives people to want to experience sexual pleasure or have one too many drinks. We all want to experience the other, and to get out of our daily existence.
Why do so many people chose to spend their whole life destroying paths they didn't even want to follow, instead of following the one path that would lead them somewhere.
You've said nothing, of course, and I ask nothing," he was saying; "but you know that friendship's not what I want: that there's only one happiness in life for me, that word that you dislike so...yes, love!