There are a few factors - whether the academics are in love with some particular language (i.e. Haskell, Eiffel, Smalltalk, or Lisp); whether there is pressure

There are a few factors - whether the academics are in love with some particular language (i.e. Haskell, Eiffel, Smalltalk, or Lisp); whether there is pressure to use a language that will help students "hit the ground running" (i.e. industry buzz words that may be obsolete by the time the students graduate, or Java/C#); and whether it's easy to teach.