Because majority of the players in this forum are Bronze-silver players that only play tanks. And tanks are the easiest to play champions both in solo-lane and in teamfights. Why would these low-elo players complain about their main, easy to play, tank champions that require the least amount of mechanical skill?
And apparently any champion that does immense amounts of damage or has mobilty to kite tanks like assasins (Zed, Fizz, Le Blanc, Riven) , Devourer junglers, Adcs like Vayne and Kalista, etc are hated by these low-elo players. It all makes sense now, this is why we see 1000s of threads about please nerf Riven, Vayne, etc daily on this Boards because these are the champions that give tanks most trouble.
But the good thing is that Riot ignores them and gives 0 fks about these nerf threads. Riot balances stuff around high-elo.