For those who didn’t know, the reading level filter allowed searchers to filter out content by basic, intermediate or advanced reading level material. This way, you were able to find content suited to how well you knew about a particular subject. So if you were an expert on a particular subject, you could filter out all the introductory material from the search results. If you were a beginner, you could check out all of the basic material on the matter.
So why did they drop the feature? It could probably be due to the fact that, although it was a cool filter, it simply didn’t get the as much use as Google wanted to see.