There are a few benefits for content owners.
First of all it’s personal besides that, they gain money from it because for some apps you have to pay before you can use them.
When you install the app, the content owners and creators also get access towards your personal information.
To end, by using an app they also give themselves an advantage. Because when a user want's to buy things online, they will first look at the apps that are already installed on their phones (like Zalando) before visiting other websites.