So how did riot decide to get rid of dominion?

Heres how they did it: they calculated how much money they would save in retiring the game mode vs how much money they make off of the people who solely play dominion. They found that they could pocket more money by doing this and decided it was worth retiring the mode. As a result, they wrote off all those people who play the gamemode because they figured that they could handle the losses, and the money they would be saving would make up for those people who they made angry because of the decision.

I think that this is incredibly shortsighted and may mark the end of the game. Mark my words, their initail profit from retiring this game mode will be entirely superficial and won't last them. What this is hurting is the new-player experience. What they may have neglected to take into account is the flow of new players into the game and how dominion might be helping them.