Definitely Not Dominion?

We've only had it three weekends since its debut in 2016 and the last time we've seen it was October of 2016. For comparison, Dark Star was introduced in May, 2017, and we've seen this mode three times already (6 weekends). It's not like Definitely Not Dominion is tied to a special skin/event like Overcharge and Invasion, so why is it removed from the RGM? I haven't been able to find any official riot announcements or forum posts about it so if someone could link me to what they said I would greatly appreciate it.