This comes from a tendency back in the mid-20th Century where the academy attempted to be on the "forefront" of musical expression and many conservatories forced their students to write in avant garde styles. And, of course, when your teacher at Juilliard speaks, you, as a young and malleable student, will surely follow and be molded to how the teacher wants. This still goes on today but to a lesser extend. Because of the increased pluralism of styles in the late 20th and now 21st Centuries, it is clear that this forcing of one specific style (or set of styles) can't work. People will write what they want to write.
Now, should students be forced out of their comfort zone and write in things which they are unfamiliar, absolutely. To take an example from my studies, my comp teacher assigned me to write a pop song with simple harmony and a secular text (since it's a Christian school there are more banal worship songs than can fit in a landfill). I did my best but it was quite a bad piece. I was simply not familiar with the genre or idiom. But I learned a great deal. Similarly, I was assigned to write a piece for electronics simply out of rhythmic elements, no pitches. Multiple meters where encouraged while loops where discouraged. This was also unusual for me since I didn't know what I was doing. I don't think rhythmically like that about my music. But it forced me to think about it in, honestly, a very clinical way. It was a good learning experience. That type of thing should be thoroughly encouraged in university.
What shouldn't be encouraged is teachers forcing students to write what the students' do not want to write on a broader scale. I know stories about students being failed for not writing specifically in an avant garde style. Conversely I've seen this happen with pro-romantic teachers at Juilliard (ironically) who failed a student for not having enough melody in their songs. Let the student write what he wants to write while making him do unusual and uncomfortable things too.