Well, first of all DeNa is the compagny who does mobile games for Nintendo if I remember right (except Dragalia Lost). This does not hinder anything about their buisness in the console space nor the devloppement of their games on the Switch.
Now, remember when people weren't willing to pay 5 measly bucks on mobile for a game like Super Mario Run just because they prefer other monetization systems ? Nintendo was willing to play a fair game by their own rules but it didn't work, then they found success in gatcha economy with Dragalis Lost and Fire Emblem Heroes which received mixed and positive results but they also saw people that were willing to completly dumb plenty amount of cash in. I guess now there just trying to see how far they can go with various monetization until they set themselves for good.
The mobile market weirdly answer positively in the context of more exploitative monetization methods in their games and that's why I always saw it as a plague most of the time.
Think it started at 10 dollars but you are right they are willing to throw down 1k on new phone yet won't drop five dollars on a game.
Most monetizations techniques are used so that the consummers don't feel pressured into making such decisions cuz spending low amounts of money multiple is more easily justifiable than paying the entry price instead which is as you'd think, scummy shit ...
Anyway, I think you may be right, it was 10 dollar at the beginning but it turned into 5 bucks shortly after a month or two if I remember ...