Probably because C++ and Java are used at the colleges s/he is familiar with.
Introductory CS courses seem to vary a lot in computer languages used (e.g. Berkeley's first three CS courses will have students using Python or Scheme, Java, C, and assembly language). It is, however, desirable for the various CS courses to use several different computer languages, so that students get used to different programming models and methods, some of which are easier to use in some computer languages than others. See The Perils of JavaSchools - Joel on Software