People plagiarize because doing the actual work is soul-crushing. How motivating is it to read a bunch of high quality work, put them together and produce a mediocre work? It's not motivating at all, and people simply try to stay sane.
And of course if you generalize the argument, then students could be excused from learning entirely. How "soul-crushing" is it for a piano student to try to play Étude in C major, when there are countless recordings of it being played perfectly, and with great genius? Following in the steps of great thinkers and doers is not soul-crushing, because you're walking in the footsteps of greatness. Those notes are the right notes. You play it badly, but you're playing it. It is humbling, though. The difference between soul crushing and humility is that for the latter, there's every reason to believe that one day you too could be great.
The other good thing about writing papers is that, no matter how expository it may be, there is always opportunity for viewpoint. Even if the viewpoint expressed has to do with how best to organize the material, every paper is a chance for self-expression.
The reason students don't like writing papers is that it's really hard. It's hard to consume the information, and it's hard to organize it, especially if you're not used to organizing information. But you have to make mistakes, write papers that are all jumbled and confused, before you can get better. Those jumbled, bad papers are clearly worse than the source material, and the teacher is there with her red pen marking the next step toward greatness.
The people writing journal papers are supposed to be doing high quality, original work, contributing to science, the knowledge of mankind, all that kind of thing.