It is not simply a matter of incentives (although they play a part). Another issue is pure publication bias. If you get 'landmark' results, a paper is much more likely to publish then if you got the results everyone would expect. In many ways this is one of the necessary functions of the journals, as it allows people to look at the new stuff without sifting through many articles of expected stuff, but it does create a bias.

Add to that the incentives of needing to get published, and constrained resources, and a willingness to publish what could be sub-par methodologys (of course they are par), and it is clearly not the best system.