Glenn Ellison has a paper in the new issue of Economic Inquiry called “Is Peer Review in Decline?” Here’s the abstract.The explanation put forward is that this has to do with the relative costs and benefits of the review process. The argument is that the editors of the top field journals, in particular, have been wanting greater revisions more often. Because the costs of the review process are high and the benefits modest for prestigious authors, they increasingly avoid these journals.
Over the past decade, there has been a decline in the fraction of papers in top economics journals written by economists from the highest ranked economics departments. This paper documents this fact and uses additional data on publications and citations to assess various potential explanations. Several observations are consistent with the hypothesis that the Internet improves the ability of high profile authors to disseminate their research without going through the traditional peer review process.
So changes in technology, the internet in particular, has altered the relative costs and benefits of peer review for the top researches in such a way that they increasingly avoid it.