The other reasons are holidays and interest in Asian culture. And also it's affordable to travel six months with not much worrying about the money. Only those two German guys who cycled from Beijing to Constantinople, which was in 1890. No other reason I guess. You're using regular track frames with steep seat angles.
Knees are all right so far.
My theory is that you get used to that gear you always push, but it kind of pushes you too, so you just pedal and you don't feel it, once you get into that mood. A lot of walking I'm telling you. So far we were really lucky with hills, because there were not much of them. In China every road goes around the hill. I miss those goddamn brakes once in a while.