While I certainly take this quiz and all quizzes with a grain of salt, I think maybe what they're getting at, at least the way I see it, is the more our life experiences have enabled us to traverse socio-economic boundaries, the more likely we are to be aware of them (duh). In other words, you may know all about Paris--you may have studied it in books and seen all the photos and the art and architecture, but you really don't KNOW Paris until you actually set foot in it. Similarly, you may know there are people who live differently from you, but limited experience in actually iving as others do will keep you from really knowing their reality.
Why does it even matter if you live in a bubble? Not sure, other than it makes it harder to understand and appreciate all sides of the prism of human experience, or to even realize there are other sides out there. I'll admit that living in the Northeast my whole life put me in a bubble, which is probably why I got a relatively low score.
Another reason for the low score is I could not say I've seen one TV or movie on the lists they gave.