You enjoy the pleasure of a well crafted machine in which all the parts work perfectly together, and if you tinker, a lot of that perfection is on you.
Your machine is so perfectly adjusted to your body and requirements that you are not aware its there, but rather feel it to be an extension of yourself.
I think @12boy nailed it there for me.
Yes, I love the freedom/health/beautiful countryside side of things, but to have a perfectly fettled piece of machinery purring away underneath me, with flawless gear changes etc really gives me a buzz.