Its not social media. My parents barely use the internet but they live in the same bubble /w fox news and conservative talk radio. Its existed for a long time, but now there are so many sources and outlets you can stay completely and entirely within the bubble.

One could argue about how much a bubble there is on the left... think for example the difference between CNN US and CNN international - one is relatively vapid lowest common denominator infotainment, and the other is hard news. I feel like infotainment/tabloidization and an uneducated populace is the biggest contributor to ignorance. Granted, its hard to know how much of a factor that's always been.

I'd love to actually see tags on facebook posts. "Extremely conservative", "Mostly Neutral", "Mostly liked by liberals" etc etc. At least make people think about why they're seeing these sources.