Why RIOT kicked out Mages off MID lane ?

I miss those days when Mid was for Mages. There were few assassins for variety but they weren't a problem as their items were on-par with AP and it required skill to play. What was the intent by RIOT to force mages go down SUPPORT lane instead of playing MID ? Can each player get an extra veto designed just for assassins role to bring some play-ability to the game?