This, in turn, resulted in a pop cultural Broken Base or Fandom Rivalry.Hip-Hop is a good example of this (see Hip-Hop's Broken Base entry).Another likely reason for this is because mainstream media is so homogenized and is prone to favoring monochrome pop culture that other cultures start their own pop-culture media outlets.That fuels this trope even further for better or for worse.
Let's face it, there are cultural barriers, and people thrive in their own microcosm.
Contrast Small Reference Pools, and Pop-Cultural Osmosis.
May lead to Germans Love David Hasselhoff or Americans Hate Tingle. This trope along with Public Medium Ignorance goes together like peanut butter and jelly. Compare with Fan Myopia, which is when the fans of a particular form of pop culture believe it to be far more well-known amongst the general public than it actually is.
Pop-Culture Isolation is basically a case of pop-culture myopia of sorts, where celebrities, music genres, media or events are huge and significant in one subculture or ethnic group, but elsewhere nobody knows they exists or is indifferent to them altogether.
We're not talking about separate countries here, but the same country or region.