The first disincentive comes from funding bodies: NIH et. al (NIGMS, NIEHS, ...) don't like to pay for you to do "someone else's science". If you manage to get a grant, and it comes out in a progress report that you did repeat too much of other people work, be prepared to get that funding reduced and or cut.
Academic departments strongly discourage new hires from publishing negative results and /or repeating other peoples work (mostly because this will likely decrease chances of getting published and funded).
Academic journals hate to publish negative results, but seemingly have no problem publishing bad science (yes Nature, I'm looking at you: http://retractionwatch.com/2014/09/11/potentially-groundbrea...). Early in my PI's career, she tried to publish a very important negative fining in a high impact journal. The article's acceptance was accompanied by a personal letter from the editor urging her to consider other journals for negative results.
Another barrier quite honestly is ego. While it may sound as if my boss is "one of the good ones", alas, she is not. On occasions that I have asked to repeat other group's seemingly unbelievable results myself, I've been flatly denied on grounds that this kind of work does not express the sort of originality of research produced by her lab. In other words, nobody wants to be known as "that lab", the nay-sayers of the field, those that would dare to question a colleague's ideas.
Finally, this lead me to the last barrier I have observed: scientific communities / societies. If you are of the lucky few that end up publishing negative results of major significance, prepare to not be invited to dinner at next years Society for X annual meeting. Yes, in many ways life-science is stratified just like high school. You have the cool kids on track for the nobel, the weirdoes in their corner pushing the boundaries of what is possible, the "jocks"/ career scientists who manage to turn a couple of tricks and some charisma into a living, and finally the tattle-tales who seem to piss everyone off with their negative results. These are HUGE oversimplifications / generalizations, but I really think that all of these barriers need to be addressed in some way to fix life science.
"There are two kinds of scientific progress: the methodical experimentation and categorization which gradually extend the boundaries of knowledge, and the revolutionary leap of genius which redefines and transcends those boundaries. Acknowledging our debt to the former, we yearn, nonetheless, for the latter."