Why Do Scientific Journals Prefer Null Findings?

When it comes to good ideas, there are two buckets in my mind. The first bucket is questions that are so interesting and important that no matter what their answer is, positive or not the answer is going to be important. For instance, do minimum wage laws have an effect on employment? No matter what the answer is, people are probably going to want to hear about it. But for other questions, scientific journal are often focussed on publishing so called positive findings. If you don't prove anything after all, why dedicate limited page space and resources to a study that didn't find anything? You can see how this creates a problem.