Few reasons for me,

1. I simply have no choice. From SIN, where I'm based at, UA only fly to NRT and HKG.
2. My threshold is about 10-hour flight. Beyond that, I get distressed and feel like banging my head to the wall, if you know what I mean. Especially when sitting in E+ in 744. (The threshold get extended when I'm sitting in UD 744, particularly ROW 15, without seatmate )
3. For food. I like to eat, and I do get hungry often. Most of the time, I could find better food inside terminals at airports than in-flight food.

Michael