Why do journals have limits on the number of references? I was rather shocked when hearing in a conversation that journals sometimes have explicit limits on the number of references that can be included in one article. I understand that there are space concerns for print publications, and that word/page limits, as well as limits on the numbers of figures and tables are common. But placing limits on the number of references strike me as rather close to impinging on the integrity of the articles themselves (would anyone support a motion to limit the number of authors?). 


  Question: What are some reasons that have led journals to limit the number of references?


Clarification: I am not asking whether this is a good idea in general. (I think it is silly, but that's just my opinion.) I am not asking whether this can have some potentially good effect on the quality of scientific writing. I am specifically asking whether there was an official explanation ever issued on the part of the publishers explaining this rule, or whether there was some event (say, an abuse in the form of many gratuitous references or an observed trend for the average number of references to keep growing if not otherwise checked) or some strong personality (famous editor-in-chief X) that led to these kinds of policies being formulated. 

For example, Applied Physics Letters has limits on number of words (with some conversion factor applied also to figures and tables), but (in my opinion, rightly) excludes the title, the author list, and the list of references from the limit. 

For examples of journals (from various publishers) that have limits on number of references:


Nature "strictly enforces" a limit of 50 for articles and 30 for letters. (Science, I note, does not for research articles. For review articles the limit is 100.)
Earth and Planetary Science Letters limits to 50. 
Blood "recommends" a limit of 100 references, though I don't know if this is a hard limit or not. 
Journal of Clinical Ontology limits to 10 for "correspondences" and a "suggested limit" of 150 for "research articles". 
Journal of Genetics (more reasonably, in my opinion), have different limits for different types of articles. But notably for research and review articles there are no limit to references: the reference number limit applies to shorter submissions such as correspondence, commentary, or "research notes". 




Some additional information: 

(TL;DR: Nature put in their current policy sometime between the years 1986 and 1988, with no reference limits prior. Did something happen in the 80s?)

I went down to the library and looked at the old issues of Nature (not because I want to single them out, but because the library happen to have all the issues since the 20s available on the stacks). After some binary search I've found that in December 1986 the instructions to the authors look like this (with no mention of limit to references)



and in October 1988 it became almost the same as present day (apologies for the flash... the lighting in the stacks wasn't good). 



(I don't have the exact date of the switch, since only some of the issues in the library came from the original magazines; others came from bound reprints ordered from the publisher which stripped out pages like these. So in particular I found no "Guides to Authors" in the 1987 issues I had access to.)

Back in the 20s and 30s most of the items in Nature had no references whatsoever. By the 50s and 60s we start seeing articles more in the form of what we expect today, but the number of references are generally not too many. Even in the 70s and the 80s (before the change of rules) the majority of the articles do abide by the modern rules, with occasional exceptions.
Journals aim to publish an organized set of articles of some approximate length in an attractive format.

Journals set limits on the number of references to shape the form, format, and quality of the submitted articles.

This organization is a good thing, in terms of disseminating scientific information. Given the limited space of one article, there is definitely some appropriate range for the number of essential and useful references that relate to the presented work.

This is less restrictive that it might sound, as these rules set by the journal are seldom hard limits. If you have good reason to include a couple of extra references, you can usually work with the editor to get them included.

Another reason to include limits is to try to encourage authors to examine references more closely, and to be more selective in their choices of what to include. Just as many journals have rules against gratuitous figures and tables (e.g. all figs must be referenced in the text), these limits are meant to discourage gratuitous inclusion of references that are not directly related to the discussion in the manuscript.



In response to the expanded question: "What happened in the 80's?" ...

The Science Citation Index was launched in 1964. With its growth and success, and the addition of other field-specific indices, it became possible to compute statistical journal and author comparisons (e.g. Impact Factor). This concerted effort to index citations made being cited in the work of others more important, and the use of numerous citations became much more common. The benefits of these author and journal metrics were much lauded during the 70's and 80's, but people were also increasingly aware that this arrangement was vulnerable to abuse, i.e. gaming the system by inflating citations. SCI grew to become Web of Knowledge, then Web of Science and along the way (1992) it was acquired by a large media company and today it's run by Thomson-Reuters.

The question posed invites speculation; we can't know exactly what the owners and editors of the various scientific journals were thinking when they started implementing citation limits. However, I would hazard a guess that they realized gratuitous citations might be an issue, probably had a few bad apples, and decided that limits were a good idea to keep the quality of the submissions high.