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Smash Bros since (and including) Melee has never been strictly about Nintendo's all-stars. It's a fighting game that has Nintendo characters. Jigglypuff has a unique enough playstyle that her spot is safe, unless they do something stupid and replace her with a Gen 6 clone. There are plenty of Melee and Brawl characters who are in because they provide a unique playstyle regardless of their popularity.
Now stop being mad that you managed to get yourself destroyed by Sing/Rest despite it being nerfed in Brawl.