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.
How I feel is that if I wanted anything I'd take it. That's what I've always thought all my life. But it happens that I want you, and so I just haven't room for any other desires.
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.
We are responsible to ourselves for our own existence; consequently we want to be the true helmsman of this existence and refuse to allow our existence to resemble a mindless act of chance.
You will never get to the irreducible definition of anything because you will never be able to explain why you want to explain, and so on. The system will gobble itself up.