Why aren't the rest of us living in space yet?

Space art from NASA made in the 1970s (find more here)

We've read and seen stories and films for decades now that suggest a future where humans will live in space. From colonizing other planets to traveling through interstellar space, many people have dreamed of a human future beyond Earth. So why hasn't it happened yet? 

After sending twelve men to the Moon in the 1960s and 1970s and supporting ventures of government organizations to send astronauts into low Earth orbit (LEO) since that time, we still don't live in a world where the rest of us can easily get into space. Of course, a large part of the argument for why this hasn't happened comes down to economics and initiative, but there are also many who would argue that we're not yet ready for it. Some may say that we need to figure out how to be better citizens of the Earth before we try to be citizens of space. 

That may seem like a flawed argument to space exploration advocates, but it's an argument that I've heard many times. I'm going to start working on another article considering what it will take to advance our human future in space, but I'd like some community input before I do that. Comment on this post or hit me up on Twitter or Facebook with your ideas about whether or not we should venture into space and why. Also, I'd like to know the reasons people suspect for why the past dreams of our future in space have not yet come to fruition. Please, tell me:

Why aren't the rest of us living in space yet?