Cause it's only three bans. 2 are for gangplank and mordekaiser, which both had a 100% win rate, and one jungler between reksai or elise, cause there are like 3 strong junglers at the time, namely; Gragas, rek'sai, and elise. If you are red side, you want to remove champions along those lines to not give blue side an advantage to get one of those 100% win rate champs as a first pick. Jungle champs would have been fine but gragas got glitched and was banned from quarter finals onwards caused the glitch was not fixed. That only leaves you with 2 strong champs: is rek'sai and elise.