Why did Riot rework Ahri the 2nd time?

Adding Q movement speed? There are definetly so many other champ that couldve been reworked instead but why did Riot choose Ahri first in the beginning of Season 5 where new masteries were being introduced? She was completely balanced then and had so much skill requirement to play, and felt rewarding to play compared to Ahri now. Ahri now, no matter how well you play, you will never have enough damage to win games. Riot nerfed her range, her damage, and sustain because of that rework, so why was the rework even kept???