In a Google Webmaster Hangout Google’s John Mueller was asked why content published on an established site tended to rank higher. The publisher asked why articles on this site consistently received “top Google rankings.”
There is no simple way to answer this question. Google’s John Mueller offered a nuanced explanation of why Google trusted some sites enough to consistently rank them at the top.
The question was asked if the success was due to a lack of competition or “is it somehow even though each individual site is a sub site of the main site, any blogging gets you ranked because” of the website itself.