Not even 100% treasure battles can help increase numbers
I think its hard to say whether this is an indictment on the game itself. Although there are some of us more "mature" players (out of college/university), I would think a large population is that age or below. In the US, this is a very busy time for that age group. Schools are either wrapping up the year with final exams or school is already out, so many families are hitting the road for vacation. Some universities have just begun their summer sessions as well.
In my case, IRL is pretty crazy right now with work and family/social activities. I don't expect I'll have much time this upcoming week to play or no the weekend for that matter. Many weddings, graduation parties, birthday parties, and trips out of town in the near future.