Data collection. More data, more targeted the ads, more income. I guess at some level, their data costs too go down with an app, when compared to a site. Also

Data collection. More data, more targeted the ads, more income. I guess at some level, their data costs too go down with an app, when compared to a site. Also, with constant notifications, apps have a better chance to become addictive. At some point, someone saw data of the time spent by users on their site, to that on app and thought, wow ! It allows for better gamification and better avenues for making users buy awards for posts. I have seen more 'gold' posts than ever after the app became popular.