To give you some perspective, there arguably weren't that many popular cartoons (other than Avatar (https://en.wikipedia.org/wiki/Avatar:_The_Last_Airbender), Foster's (https://en.wikipedia.org/wiki/Foster%27s_Home_for_Imaginary_Friends), and SBSP (https://en.wikipedia.org/wiki/SpongeBob_SquarePants)) with most of this era's fare ranging from forgotten (Jake Long (https://en.wikipedia.org/wiki/American_Dragon:_Jake_Long), Chowder (https://en.wikipedia.org/wiki/Chowder_(TV_series)), Danny Phantom (https://en.wikipedia.org/wiki/Danny_Phantom)) to absolute garbage (Johnny Test (https://en.wikipedia.org/wiki/Johnny_Test), Fanboy and Chum Chum (https://en.wikipedia.org/wiki/Fanboy_%26_Chum_Chum)).

Several factors for why such a thing likely happened (http://tvtropes.org/pmwiki/pmwiki.php/DorkAge/WesternAnimation) include Disney abandoning animation, Cartoon Network becoming over-reliant on live-action (http://tvtropes.org/pmwiki/pmwiki.php/DorkAge/TelevisionNetworks) and Canadian acquisitions, and Nickelodeon (http://tvtropes.org/pmwiki/pmwiki.php/NetworkDecay/MajorShiftsThatFit) starting to mistreat their cartoons in general.

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Pretty much any animation made after 2000 is part of the "Dark Age" of animation(with exceptions of course)