I can't read the full article without signing up there but Pokemon Go was really scuppered by its design and difficulty level. I was well into it with the kids but after a while leveling up takes months and it's almost impossible to catch the rarer ones.
I think they could have sustained it with quicker updates so they added more to add but they took a long time to do it and enthusiasm had worn off. It's a problem with a lot of viral games, you don't have to be easy but you need consistent progress. I got into Farmville at one point as it was fun but two months in and I realised it was taking me 30 minutes to collect the crops and was becoming a full time job so ditched it.
I think that's where the Candy Crush guys have done better in the casual games, you can keep going without hitting a point where it's either impossible or becomes a chore.