Right now you have a "reproduction renaissance" in psychology and cancer, where you can get published, and get acknowledged, if you tear down a high level paper. But in general, unless you aim at refuting the highest level, it is hard to get published and advances your career nowhere, so people have no incentive to do it.
Edit:
When I did medical research I wished people would try to replicate my findings so I could see how consistent the results were and how well my model fit future data... In fact it was really annoying that it was unlikely anyone would ever try to do a direct replication.
A single non-replication does not. Consistent failure to replicate, after communicating with the original author, does.
See e.g.
http://www.slate.com/articles/health_and_science/cover_story...
http://www.nature.com/nature/journal/v483/n7391/full/483531a...
Or just google "reproducibility crisis", the two most common subjects that come up are cancer research and psychology research.
Because the incentives are to provide "new research", not to confirm or deny a known result.
It seem to me that most probably no-one has gotten tenure by reproducing, disproving results.
This seems like something an amateur could do. Wouldn't that tear down a bunch of this junk?