Besides Human beings being self-centred jerks most of the time, the only other reason I can think of is that certain strategies or game styles that counter champions cannot be accomplished as easily in lower ell's / soloQ.
Teamwork trumps all, which is why the pro teams that practice together so much can effectively counter any champion. This is the reason why Master Yi's and katarinas just pub stomp low elo's/solo Q's because there, no one can chain cc or communicate as easily as the pro teams with their comms or higher ell's with their game sense.
Hence, the elo hell. Where any champion that thrives in chaotic fights against unorganized enemies are super strong. In order to balance these champions to make them viable in higher elo's, Riot has to buff them which to the bronze and silvers seems like strengthening an already "OP" champion.
Riot balances to LCS levels but since none of us have the pleasure of being in constant communication or choosing who we play with every game the balance seems unfair since we don't have the teamwork or communication to make that balance apply to us.