I suspect Fire Emblem Heroes is a result of competing interests inside Nintendo. Miyamoto has said publically several times that he doesn't think they should be making games like that—even after Fire Emblem's success: https://gamedaily.biz/article/197/nintendos-shigeru-miyamoto...
I think it has been financially successful—but when the WiiU was failing, Nintendo needed a backup plan, badly. Now that the Switch is incredibly successful, they’re not as desperate for a Plan B, and so mobile ports are mostly a distraction, even if a profitable one. But their biggest bottleneck is time and developers, not money.
I'd -gladly- write games (and software) for the switch if it was a more accessible platform to develop for.
Developing software for Nintendos previous platforms was difficult for anyone who didnt have 'connections' in the industry.