Google does not allow apps within the app store to present their own payment method, except for Spotify which is part of some trial right now.
I could definitely see shady apps within the stores collecting payment info from users that then use those cards as if they were still on. If people get used of apps collecting payment information on all different kinds of UX, they will likely be more willing to type in their information into any app, leading to a higher chance of stolen payment information.