Comment by mrandish

> the web interface is like right there staring at them.

True but the an app gives Facebook much more user data for targeting which dramatically increases revenue per ad. Persistent user data that's largely unconstrained by privacy safeguards is the holy grail. The mobile browsers are also controlled by Apple and Google, so despite the web being 'open', when one of them makes even minor changes to increase browser privacy defaults, it can have major impact on Facebook's revenue.