It's way easier for the developer of the app to steal data in the native app.

Trick user to open FB or any site. Open the requested site in the built-in browser. Let user login to the site, and then scrap all the information. Apple and Google can't stop that.

You can't do that in the browser.

> A native app could leak/abuse information like a web app, but in general the surface area is way smaller for that to happen on iOS