There are multiple reasons. The image is iconic, famous and is one of the few true photographic images of Earth. It has also been a featured image since November 2004. Other images may present more detail of the land masses, but they are generally composite or processed images. For some previous discussions see (1234567).
Q.
Why does the article not have mostly harmless as its short description or otherwise summarize the article's content using it?
A.
This has been discussed several times including (12345). The consensus is that it fails WP:42.
This article is written in American English, which has its own spelling conventions (color, defense, traveled) and some terms that are used in it may be different or absent from other varieties of English. According to the relevant style guide, this should not be changed without broad consensus.
This article is within the scope of WikiProject Astronomy, which collaborates on articles related to Astronomy on Wikipedia.AstronomyWikipedia:WikiProject AstronomyTemplate:WikiProject AstronomyAstronomy articles
This article is within the scope of WikiProject Geography, a collaborative effort to improve the coverage of geography on Wikipedia. If you would like to participate, please visit the project page, where you can join the discussion and see a list of open tasks.GeographyWikipedia:WikiProject GeographyTemplate:WikiProject Geographygeography articles
Talk:Earth is part of WikiProject Geology, an attempt at creating a standardized, informative, comprehensive and easy-to-use geology resource. If you would like to participate, you can choose to edit this article, or visit the project page for more information.GeologyWikipedia:WikiProject GeologyTemplate:WikiProject GeologyGeology articles
This article is within the scope of WikiProject Science, a collaborative effort to improve the coverage of Science on Wikipedia. If you would like to participate, please visit the project page, where you can join the discussion and see a list of open tasks.ScienceWikipedia:WikiProject ScienceTemplate:WikiProject Sciencescience articles
This article is within the scope of WikiProject Culture, a collaborative effort to improve the coverage of culture on Wikipedia. If you would like to participate, please visit the project page, where you can join the discussion and see a list of open tasks.CultureWikipedia:WikiProject CultureTemplate:WikiProject Cultureculture articles
This article is within the scope of WikiProject Spoken Wikipedia, a collaborative effort to improve the coverage of articles that are spoken on Wikipedia. If you would like to participate, please visit the project page, where you can join the discussion and see a list of open tasks.Spoken WikipediaWikipedia:WikiProject Spoken WikipediaTemplate:WikiProject Spoken WikipediaSpoken Wikipedia articles
Complaints about the lack of young Earth creationism or similar points of view are inappropriate content for this talk page. For an overview of Wikipedia's position on creationism or young Earth-related topics, please see the FAQ at Talk:Evolution.
This article has been viewed enough times to make it onto the all-time Top 100 list. It has had 76 million views since December 2007.