Citing a problematically small active playerbase for the mode, Riot Games announces they are dropping the Dominion game mode from League of Legends after a four-year run as an alternative challenge for players of the MOBA. They describe the mode's death spiral that's prompting the move:

We want to support game modes delivering consistently engaging and competitive experiences. Fewer than 0.5% of players actively play Dominion and we’re aware some number of even that small population is still bots. We haven’t been supporting Dominion, and we’ve trapped ourselves in a vicious cycle where the queue isn’t large enough to warrant major attention, but falls prey to bugs and periods of imbalance from the introduction of new champs and items (which then drives down the size of the queue, and so on).

In the absence of our attention, matchmaking and game quality in Dominion varies wildly based on daily engagement. Because of how matchmaking works, the longer someone looking to play Dominion waits in queue, the wider the pool of potential foes the matchmaker can pull from -- with such a small population, Dominion games can match up widely divergent skill levels after long enough queue times. Unhealthy queues that force players to endure long waits with fluctuating match quality ultimately creates an overall poor experience -- one we take responsibility for.

We might have been able to break out of that downward spiral with more dedicated resources, but we chose Summoner’s Rift as the core League of Legends experience with its depth of gameplay, match pacing, and path to mastery. When it comes to the resources required to keep Dominion permanent and solve the inherent design problems and give it ongoing live balance support, we’ve consistently devoted them to Summoner’s Rift and related features because we felt they’d improve the overall League experience more.