I heard that they are gonna DESTROY the online service and I know Game Freak made it that way but why. And someone´s gonna say "X and Y is now popular" or something similiar
well, its just that xy has become popular now, and 98% of the competitive Pokemon fans has probaly already bought xy and doesnt play gen 5 anymore, so it would be too expensive for Nintendo to support something that almost no one Plays anymore.
Nintendo has announced that, as of May 20th 2014, all online services across the DS and Wii games will terminate. This means that you will not be able to go online with any of the following Pokémon games: Pokémon Diamond, Pokémon Pearl, Pokémon Platinum, Pokémon HeartGold, Pokémon SoulSilver, Pokémon Battle Revolution, Pokémon Black, Pokémon White, Pokémon Black 2, Pokémon White 2, My Pokémon Ranch, Pokemon Mystery Dungeon: Explorers of Time, Pokemon Mystery Dungeon: Explorers of Darkness, Pokemon Mystery Dungeon: Explorers of Sky, Pokemon Ranger: Guardian Signs, Pokemon Ranger: Shadows of Almia & Pokémon Conquest. All online features of these games will be inaccessible, regardless of the console you play them on. All 3DS and Wii U games will continue to be playable online, as will Pokémon Bank and Poké Transporter.
Source: Serebii