Revive the dead champs

Why are RIOT nerfing so many champs to their death. Right now League Of Legends is most of time a meta game, based on there is some strong champs(The meta champs) and weak champs. If u try to pick the weak ones and isnt lvl 7 mains with them, u just get fucked. The meta champs are basicly the easiest(Annie, Amumu, Trynd and that kind of champs), then there are the overbuffed( Kog'Maw, all champs there is useful with ardent censer, tanks and tank counters) and last but not least, the overscaling champs, that is way too strong( Cho'Gath, Fizz, Katarina etc.) But it's sad to think that all the fun champs, with the fun skillshots and awesome gameplays are dead):