Reasons:

SEO Best Practices - Avoiding Duplicate Content

Search engines like Google have a problem – it’s called ‘duplicate content’. Duplicate content means that similar content appears at multiple locations (URLs) on the web, and as a result search engines don’t know which URL to show in the search results. This can hurt the ranking of a webpage, and the problem only gets worse when people start linking to the different versions of the same content. - Yoast

Avoiding Possible Google News Implications

If the URLs of your main news sections change on a daily, weekly, monthly or quarterly basis, we may not be able to include your site in Google News. Non-permanent URLs prevent us from crawling your new content, as we’re unable to detect the most current URL to be crawled. Our automated crawler is best able to crawl sites when the URLs of your main news sections do not change.

Story Type Page:

io9.gizmodo.com/c/television automatically loads gizmodo.com/c/television

Category Page:

steamed.kotaku.com/c/review/video-games automatically loads kotaku.com/c/review/video-games

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Sub-Category Page:

steamed.kotaku.com/c/review/video-games/pc-exclusive automatically loads kotaku.com/c/review/video-games/pc-exclusive

Tag Page:

tv.avclub.com/glow automatically loads avclub.com/glow

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