What I don't know

I'm a novice when it comes to backpacking. I have been on many hikes, but usually end up driving home or settling down at the campsite once the trail ends.  I hope to learn more about thru-hiking.  Thru-hikes are done on trails that may reach up to 1,000 miles or more.  I would like to know why people subject themselves to these hikes for such long periods of time.  Why would someone want to isolate themselves from everyone else for weeks at a time?  Even if they don't go alone, which I wouldn't try, being around the same person for that long of a time could cause some problems.  Another question I have is how can people afford to leave their homes, families, and jobs for these trips?