It was the social graph that made Google Reader great not the basic RSS functionality. That was really the game changer. It tapped into your friends feeds, what they liked and read.

You could follow other peoples recommendations, and the user belonged to a network of other users. It also made finding widely shared news items stand out and interesting blogs to follow easier and strengthened the network by doing so.

All the replacements afterwards didn't have this social aspect (or if they did they lacked the network needed for it) so they were like a graveyard socially.