|This page in a nutshell: When citing material in an article, it is better to cite a couple of great sources than a stack of decent or sub-par ones.|
These are probably too many sources to cite for a single point.
Wikipedia policy requires all content within articles to be verifiable. While adding inline citations is helpful, adding too many can cause citation clutter, making articles look untidy in read mode and difficult to navigate in markup edit mode. If a page features citations that are mirror pages of others, or which simply parrot the other sources, they contribute nothing to the article's reliability and are detrimental to its readability.
One cause of "citation overkill" is this example illustrating an exaggerated case of citation overkill.
Another common cause of citation overkill is simply that people want the source they've seen to be reflected in the article too, so they just tack it onto the end of existing content without making an effort to actually add any new content.
The purpose of any article is first and foremost to be read – unreadable articles do not give our readers any material worth verifying. It is also important for an article to be verifiable. Without citations, we cannot know that the material isn't just made up, unless it is a case of common sense (see WP:BLUE). A good rule of thumb is to cite at least one inline citation for each section of text that may be challenged or is likely to be challenged, or for direct quotations. Two or three may be preferred for more controversial material or as a way of preventing linkrot for online sources, but more than three should generally be avoided; if four or more are needed, consider bundling (merging) the citations.
Not only does citation overkill impact the readability of an article, it can call the notability of the subject into question by editors. A well-meaning editor may attempt to make a subject which does not meet Wikipedia's notability guidelines appear to be notable through quantity of sources. Ironically, this serves as a red flag to experienced editors that the article needs scrutiny and that each citation needs to be verified carefully to ensure that it was really used to contribute to the article.
Misuse to prove an obvious point
It is possible that an editor who is trying to promote an article to GA-class (good article status) might add citations to basic facts such as "...the sky is blue...". While this might be a good thing in their eyes, the fact that the sky is blue does not usually require a citation. In all cases, editors should use common sense. In particular, remember that Wikipedia is not a dictionary and we do not need citations for the meanings of everyday words and phrases.