Cash app: 

1) available to 350-700 million out if 8 billion people
2) requires gov ID - billions dont have this
3) requires modern device - billions dont have this
4) requires fiat rails - billions dont have this
5) requires fiat bank account - billions dont have this
6) requires email + pw - extra friction

It may be easy for nostr:npub1r0rs5q2gk0e3dk3nlc7gnu378ec6cnlenqp8a3cjhyzu6f8k5sgs4sq9ac 

Not for most of world.