Because whenever someone has a really big result, they try to publish it in Nature or Science. By their very nature, big results are more likely to be wrong th

Because whenever someone has a really big result, they try to publish it in Nature or Science. By their very nature, big results are more likely to be wrong than small, incremental results. The main reason why Nature is prestigious is because getting published there means the scientific reviewers and editors think your result is really important.