All the APPS have a cycle,
usually involving
A) profitability
B) user numbers
when they first come onto the scene, it's free and seamless, and AD FREE, they need user numbers to go up, and they do. But, once someone has an app and it becomes part of their daily life, they are less likely to delete it and so they introduce ads. Tweak the algorithim.
then it becomes less popular. people move to a new one, which does the same thing.