>>30602087"Pokémon Chronicles" was not a separate series. They were the special side episodes that would air periodically for Pocket Monsters Encore and Weekly Pokémon Broadcasting Station, which were the predecessors to Pokémon Sunday, Pokémon Smash!, Pokémon GetTV, and Pokénchi. The side episodes (still released to this day) would all fall under the Pokémon Chronicles banner if they still released it as such.
http://bulbapedia.bulbagarden.net/wiki/List_of_side_story_episodesThe Origin was a promotional stunt for X and Y. All four episodes aired in one sitting in Japan, and were not planned to air again.
Generations not having a Japanese release is odd because the interest has been shown to be there in Japan. There have been plenty of posts in Japan asking why ポケモンジェネレーションズ is available in all languages but Japanese, and there are Japanese-subtitled English dub videos out there. Like I said here
>>30601912, its main goal is to be low-cost, low profit fanservice to older fans in order to promote the franchise.
It was actually thanks to the animated B2W2 promo that we have The Origin, Generations, and the ORAS promo, because they saw how critical reception among older fans was much more positive. Still, it's not worth it financially to drop Ash and appeal to just the older fans.
