Sending money to friends/family around the world is still a lot more difficult than it should be. Facebook is already the central hub for lots of families and communities, so being able to easily send money over Facebook would be nice, and having that tied to a specific traditional currency would be a bit inconvenient.

Hmm. That makes more sense now.

Make FB a platform to exchange money globally.

If successful, FB can reap billions in transaction fees to allow users to transact on their platform, be it for money transfer or for ecommerce.

I would not be surprised if Zuckerberg sees a future where the reserve currency is a digital one instead of the USDollar, where global currencies are valued in relation to Libra, rather than the $

WeChat Pay

> Facebook provide health insurance or a grocery store

Amazon does both of those. (some) Modern tech companies want to be everything platforms.

Facebooks business is ads. Facebooks largest growing market is the third world. Ads are worthless there because people have no money to spend on sh*t they don't need. Now if FB makes micro transaction possible and cheap and even available for the unbaked, suddenly the poorest of the world are potential customers and thus can be targeted with ads. They may only have fractions of dollars to spend but they are literally billions so it ads up.

TL;DR Banking the unbanked with cheap micro transaction makes them milkable.