If you ask me, the first thing is that the game hardware is not rich. Only one of Mario's new works caught people's eyes when it was released, and the others were old works of fried rice. There is no exclusive new game to keep up with in the later period. Why don't gamers buy games?
The second point is that Nintendo's first-party game is too tough, and the third party has never been popular on any platform, which makes the relationship between Nintendo and the third party very hard. Not many people want to develop their works on Nintendo's platform. Most players who buy any console just want to play Nintendo's own games.
The third point is that Nintendo has always been stubborn, ignoring social networks, dead house and rotten women, players from other parts of Asia, and young senior players, thinking that a few Mario Zelda can play all over the world.
Above, personal opinion.