There have been some incredibly successful smartphone games made using Nintendo franchises, but a lot more money could have been made if Nintendo hadn't been adjusting their games and reigning in the business practices of the developers that they worked with, in order to prevent players from spending too much money.
The smartphone game industry has exploded in recent years, with titles like Candy Crush Saga and Pokémon Go bringing in millions of dollars each month. Nintendo eventually buckled under the pressure of their shareholders and allowed smartphone games to be made using iconic Nintendo franchises, which has resulted in games like Animal Crossing: Pocket Camp, Fire Emblem Heroes, and Super Mario Run. Nintendo's smartphone games share a lot of the gacha gaming practices used by other smartphone games (except for Super Mario Run) but they are not as bad as other prominent titles on the market and it's possible to enjoy Animal Crossing: Pocket Camp and Fire Emblem Heroes without ever spending a dime.
It seems that Nintendo has been holding back the smartphone developers that they have been working with in order to stop the players from spending too much money, which has been great for their public image but has caused issues with their business partners. According to The Wall Street Journal (hat tip IGN), Nintendo has asked companies like CyberAgent and DeNA to adjust their games in order to limit the amount of cash that a player can spend.
Nintendo sees their smartphone games as a way of promoting their video game brands and they are limiting the revenue they can make from their mobile endeavors in an effort to avoid looking greedy and maintain their positive public image. When Dragalia Lost was released, there were complaints about the scarcity of rare items, which prompted Nintendo to ask CyberAgent to adjust the rate at which those items dropped in order to make them easier to acquire.
Nintendo's business practices don't seem to have had a negative effect on their upcoming plans for smartphone games, as they recently announced that Dr. Mario World would be coming to mobile phones in 2019, with Mario Kart Tour also planned to be released in the summer. Nintendo has also started recruiting developers for a new Pokémon smartphone game that will try and repeat the incredible financial success of Pokémon Go, which has brought in over a billion dollars since it was released in 2016.
It's odd to see a company not trying to milk its audience for as much cash as possible in this era of battle passes, loot boxes and microtransactions, but that's exactly what Nintendo is doing with its mobile ventures. Nintendo has access to some of the most recognizable video game franchises in existence and the company could have easily greenlit a bunch of cheap cash-in titles in order to make money off the mobile gaming boom, but they have held back in order to maintain their image, while companies like Square Enix will throw any of their iconic series onto a mobile phone for a quick buck.
It's also possible that Nintendo is behind the times as normal and has been missing out on an amazing opportunity while people are still paying money for gacha games and that the mobile gaming bubble will burst before they catch up, but it's hard to fault the company for not wanting to squeeze as much cash out of their fanbase as possible with shady mobile gaming practices.