App Store is 14 years old. If Apple wanted to take a cut of literally everything that was facilitated using the phone e.g. Amazon or eBay they would've done it a long time ago.
The benefit to Apple is the same reason that Google invests in Project Zero.
Higher consumer confidence that a product is safe = higher engagement = higher revenue.
Here are a few of the emails I was mentioning:
https://www.twitter.com/techemails/status/148133934582287974...
Based on the emails that have come out from various trials, they want a 30% cut of everything, eventually including real world services mediated through the phone.