I think it's just that it's interesting to look at critiques of political systems. Adam Smith doesn't have the same name brand when it comes to Capitalism that Marx does when it comes to Communism, so it's easier to see posts about marx and communism more generally.

I find it interesting, personally, to see how different the modern day conceptions of these two schools of thought are from their origins, and how they contrast with the views of their originators.