To start with, CS students are not the masses.

In addition to that, some CS students at some schools are exposed to the linux command line, and even less are exposed to linux desktop environments because most CS students have grown up using Windows or Mac and the curriculum is nearly always structured in such a way that it is unnecessary for the student to install a linux DE in order to do their work.

Finally, I'm not willing to blindly accept your claim that "very few of them still choose it", if you have some way to substantiate that claim I'd be interested in the details, but my experience says quite a few of them do choose it, though I'd certainly be willing to yield my anecdotes to some actual data.