Many people drop out of high school for various reasons, that we can all agree on. Sometimes it's for family reasons (one friend had to drop out because his parents disappeared and he ended up having to look after his little sister), sometimes it's for personal reasons (one kid got knocked up in grade 11 and she decided to carry it to term, but felt she wasn't able to do that
and school
), and sometimes it's for something else (another friend from elementary, one of the smartest kids I know, ended up falling in with the wrong crowd and got hooked on drugs... after which he got kicked out of his house and I haven't heard about since). I know more people that dropped out, but those are the three main reasons for why they all did.
The thing is that while a couple of them are actually successful (trades and rig pigs), most of them aren't. They live paycheque to paycheque at their McJob or rely on EI because they're used to not working for their money. Yes, there will always be a Steve Jobs type story talking about how some random drop out is now making more than someone with their PHD in science, but these stories are rare and not indicative of how real life works. As some people have said, getting a solid career is all about hard work and networking. Sure, you can start off as an order picker at a warehouse and eventually work your way up the chain, but it takes hard work. When you go to school, you and your peers all network with one another. I know I certainly did when I went to Capilano College for film work. If it wasn't for all my fellow students being able to network with each other, many of us wouldn't have been able to get our foot in the door for film work. And, as someone else mentioned, many people wont even consider your resume if it doesn't state that you've graduated from high school.
That said, many people who finish high school and go to University are just as much of a lazy ass as those who don't. I know a few people who went to UBC without a clue as to what they wanted to do and simply ended up with a random BA because they chose easy courses. Yes, a few of these people actually ended up being able to find respectable careers with them, but most of the rest are working at places like Starbucks.
I wouldn't go around categorizing drop outs as losers with no focus in life, but, yes, they definitely have a harder hill to climb if they want to make something of their lives.