For example... maybe one scientist pays another scientist to reproduce his work. Maybe you have big collections of graduate students that as part of their process of getting a degree get assigned some random papers submitted by scientists in their field and they have to reproduce the work.
You don't work in science do you? Being paid for reproducing someone else's work means you are not producing anything original of your own. It doesn't advance your career. Then with respect to your second point, being a graduate student means to perform original research. If your PhD is about reproducing someone else's work, you won't be able to publish anything of significance.
The problem is the system globally: journals, which push for high impact sexy stories; promotion committees, which only look at how many high impact papers scientists have published and at how much funding they have attracted; and finally funding bodies, which only look at publications. If you are not lucky enough to get into a big lab which automatically publishes in high impact journals based on the labhead's reputation, the incentive to game the system is high. You just need to look at all the scandals that have come to light in the last years. You can even buy authorship on papers to which you have contributed nothing (http://www.sciencemag.org/content/342/6162/1035.summary).