Good score no S

MagicSheld - Summoner Stats - League of Legends
MagicSheld / Gold 4 0LP / 180W 145L Win Ratio 55% / Darius - 24W 12L Win Ratio 67%, Thresh - 22W 8L Win Ratio 73%, Aatrox - 12W 10L Win Ratio 55%, Lee Sin - 8W 13L Win Ratio 38%, Corki - 11W 5L Win Ratio 69%
So I'm not sure why but even if I got good score with Lulu, I never seem to be getting any S. The link leads to my match history, I'm wondering if the requirement of getting an S like least an S- has raised, or it's just my score isn't good enough.
Report as:
Offensive Spam Harassment Incorrect Board