Why to travel, is simple answer: to see other places. But here comes the difference: How to travel, and why you do it like this? You can travel to everywhere with plane, and eat only your cultural food, go to museums, and follow travelling guidelines. It could be great trip too, but I think it just gives people a change to cross out country name in some "bucket list". "oooh, wow, you have been in Spain?" or smth. But besides the "i was there" feeling it does not give so much difference than just siting at home, reading traveling books, and watching pictures.
But why to travel in alternative way? To FEEL other places, to have experience. Getting feeling of other cultures. And most of all: what it all says about you, as well. We all know sterotypes, and have some kind of imagination (not that word I need, but sorry for my bad english

) what some country would look like, or people there... but is it always right? I doubt about it alot.
If you hitchhike, and stay in locals place, you will get the point how people actually are thinking. How often are you able to talk with foreigns in your country? And eating in some countries resturants gives us idea of the food, what sells. Do they really make that kind of food, what their own country people really like, or what gives them a thought that this is what people want to buy? Every country sells something "italian" or "french", but go to actually italy, and people will tell you that they don't like this BS at all (at least not like this, how it's in markets).
Or politics. News give us false imagination how some countries are, although it's just state what thinks like this, not its people. Visit local family and see how father reacts to their politicans decisions.
So, shortly: just to break sterotpes, and prejudices, and get experience.
About self learning: just to get out of your comfort zone. To find out how you could handle some situations. Even if you don't have "normal" (for our society) life: you live on the streets, for example, it's still easier at your own hometown, where you know people and places. What time shops will be closed, where its easy to dumpster dive, how cops will react and so on... But ending up totally broke in unknow place: a nice way to learn about life, and you.