My off the cuff answer was “I like to see what’s on the other side of the hill”. Others have written their answers much more eloquently but my more complete answer would include things like:
Exactly what is on the other side? The modest pace of a bike truly allows one to see, smell and hear the country side one is passing thru. But unlike walking or hiking, that same modest pace will get you across the valley in front of you and into that distant mountain range by the end of the day.
Independence and self-reliance: I love the feeling of pedaling to some distant, unfamiliar location with a fully loaded bike. Knowing I have all the gear and food needed to be able to stop and camp anywhere, anytime I decide to end my day.
Watch the sun come up and go down: I like knowing that as I climb out of a warm sleeping bag to a lonely, chilly dark morning that soon I will see the sun rise and feel it warm my freezing face, hands and feet. As the day progresses I might see a fellow racer and share some experiences. Later in the day I could have a solitary snack, sitting on a rock with a view to forever. As the sun goes down and the temperatures fall my body will come alive and for a few brief hours I can hammer the pedals with the knowledge of coming respite. After the sun sets, following the pool of light from my headlight I will search for (and never truly find) that perfect camping spot. Soon fatigue will force me to ‘just pick a spot’ and stop.
Solitude and Companionship: I like the quite flow of a day spent entirely alone, self-contained within my own rhythm and thoughts. The TDR might give me day after day of this type solitude, yet also the random chance to spend time with fellow racers. The possibly of shared experiences and a break from the loneliness that creeps in go hand in hand with the solitude.
Typical challenge & competitive drive stuff: I like the preparation and challenge of the TDR. I am totally engaged, even obsessive about preparing for this race. And specifically I like to finish ahead of younger, faster, stronger riders by being more efficient. I truly am a relatively slow/weak bike rider compared to 90+ percent of my fellow racers. And in a long multi day race, being more efficient can add up to surprisingly results, surprising to me at least.
Riding a bike: Hey, I just like riding my bike, and to be able to do it all day long in combination with the above mentioned reasons adds up to true enlightenment.