Why do 90% of schools teach Of Mice and Men?

UK Education Secretary Michael Gove has again noted that the vast majority of school children study John Steinbeck's novella Of Mice and Men. Why?

Source: http://www.bbc.co.uk/go/rss/int/news/-/news/magazine-12829392

usgs frankie edgar vs gray maynard wynton marsalis unclaimed money treasurydirect