Call me cynical, but the whole idea of Libra would be disruptive to the existing international payment businesses, such as the ones that just exited. So the only reason for them to join in the first place would be to basically "know your enemy" - make certain you get the first-person intel on the project's vitals and to know what to expect. Now that a couple of governments made it clear that there would be roadblocks in deploying Libra according to the original roadmap, it is no longer seen as a threat, so anyone without a direct monetization interest (Facebook itself?) is going to leave.
I'd argue the real reason behind it is to skirt GDPR-like privacy laws. If microfees are used for certain interactions, even if they are negligible amounts, Facebook would be required to retain the data attached to it as it's part of the transaction.
