To me there's something deeply appealing in what they're doing. Perhaps it's the concept of being totally self-reliant, unhurried and able to rest your head wherever you find yourself. I imagine that it must be a kind of meditation, legs pumping away automatically, the mind in a heightened state of awareness ...
It's not all fun and games though - a few I've spoken to have told me scary stories of encounters with robbers, thugs and suspicious, abusive government officials in some countries.
I salute these intrepid adventurers.