The problem is compounded because while I've been logging on daily and participating, as my friends slowly drop off there's less for me to do and fewer people to interact with and much less incentive for me to come back the next day.
It should have had the ability to add friends over SMS from day one. I downloaded it on day one and my sister did too. However, since I have Android and she has iOS, the methods it launched with to add friends didn't work. If I could have added my sister as a friend, I probably would've been more interested in continuing to play miitomo.
That behavior is the case with every social network. (which is what Miitomo is categorized; it is not in the Gaming category)