I think it was unsustainable. Especially depending on how you're defining "enthusiasts." If we're talking about enthusiasts who still actively play the latest

I think it was unsustainable. Especially depending on how you're defining "enthusiasts." If we're talking about enthusiasts who still actively play the latest and greatest Pokemon games, Pokemon Sun and Moon only sold about 15 million units last year when it came out. (Probably a couple million more have sold since, but I can't find any up to date numbers.) To still have 50 million more active users than units sold of the latest core franchise game I think is pretty good. As for the nostalgic enthusiasts that you're probably thinking of more, I would still think that those who play the old games are much fewer and farther in between. I'd be surprised if there were still 650 million people picking up old Pokemon games. Pokemon Go was a nostalgic fad that everyone and their mother (and some grandmothers) decided to pick up because it was the cool new thing. Not saying that Niantic didn't drop the ball early on--they did. But even if they were on the top of their game, I still don't think of the 650 million downloads that they were going to be able to retain a majority of those users.