I think the reason that Nintendo's shutting down the game is because they aren't making a profit. Yes, crap is happening around the gaming industry as we speak.
But being logical, I heard they only made a couple hundred million dollars on microtransactions on this game, while Fire Emblem Heroes has generated over $1 billion.
There are no ads in the games, Gold Pass yearly costs 3 times the amount of a yearly normal online subscription... With there being lawsuits and criticism with the ruby system, I'm sure that there's reasons for this. Oh, and the names foe CPUs being of random player's names.
Super Mario Run has been going on for longer, I guess they still run it because they use it as a tool for marketing new Mario games, and also it has a onetime fee to start playing. Tetris 99 does the same thing with games.
Super Mario Run has the Toad rallies, however I would guess that running stuff like Mario Kart Tour takes up more resources since it has things like a online mutiplayer... I wish they made an offline version for Tour like they did with Animal Crossing, but I guess that would require some maintenance as well for bugdixes