In an announcement posted on its website, “Miitomo will end its service at 12:00 AM (PDT) on 5/9/2018, and we want to thank you for your support since the Miitomo app’s launch. Until the end of the Miitomo service on 5/9, we’re offering daily login bonuses of Miitomo coins and game tickets so that users can continue to play Miitomo Drop and use other features such as the Miitomo shop.”
While the Miitomo app did see a fair bit of success when it first launched (presumably due to curiosity), subsequent reports indicated that the game was losing players at a steady rate, claiming that the lack of updates and progression as being one of the reasons. The game wasn’t so much a game but a social app of sorts where users could interact with each other in a virtual world.
Following its release, Nintendo has since put out titles like Super Mario Run, Animal Crossing, Fire Emblem, and so on, and it is expected that more such titles will be released in the future.