When you have something disruptive to your monetary industry which offers control over other people, analogous to a religion, you would want to remove it as quickly as possible.
I'm not really certain that libra would disrupt much of anything, and there have been doubts in my mind as to whether it would achieve much adoption, unless facebook *forced* it on people, requiring that they use it instead of fiat.
Facebook is the largest network in the world. What better foundation could you build a payment network from?
At the very least, it would disrupt the remittance industry in a big way because they could offer massively lower costs than firms like Western Union.
I don't think most people have a problem paying for things online with fiat, except the unbanked but there hasn't exactly been a groundswell of people demanding that someone create a stable coin that they can use for...whatever.
People pay out the ass for international remittances. That's who Libra was targeting. If I used Western Union to send $100 to China right now, they would take 10-11% in fees.