Well, there could be many reasons. First off, there are many different historical and cultural differences between Shakespeare's time and modern times that a modern student doesn't pick up on, doesn't understand.
Second, you simply have to take into account the fact that, with modern technology, students' attention spans have gotten so bad that simply reading Shakespeare plays is "too boring" for them.
Modern students want quick answers, a bubble they can circle on a multiple choice test type of answer. Interpreting Shakespearean plays requires thought and critical thinking, things that, I'm sorry, but no students seem to use nowadays.
Also, there is the small fact that, especially amongst teenage males, things like plays and reading Shakespeare are labeled as feminine or "gay".
