I can't speak for everyone else, but when I left home at 15, I didn't do it because I *wanted* to or cuz I thought it would be fun to travel. Hell I didn't know what the fuck I was even doing. I left home, because my home life (to say the least) was unacceptable. I didn't wanna be on the streets and homeless back then. I wanted a roof over my head and a family that loved me. But that's just not how it was for me. I went to a greatful dead concert in Pittsburgh Pa and ended up getting into a van of hippies and road across the country with them for awhile, and wound up in New Orleans where a group of gutter punks took me under their wing, and basically taught me about street life. How to spange/fly signs, where to squat, about feed's and free shower's, etc. I was a fresh faced kid that knew nothing about street life, and I'm still greatful to this day for those kids who taught me what was up, and how to not be so damn naive.
Now when I travel, I do it because I want to. Nothing like the wind in your hair, and a little piece of freedom. But it's my CHOICE these days. It isn't something I have to do out of survival.