Why doesn't Zuck make libra into real money?

Why bothering with fiat exchange at all, let that be done by third parties.

Instead sell Libra S/L licenses world wide, along with the Zuck pay protocol?  Exactly like I discussed with BTC, except skip BTC all together.

Each Libra S/L can resolve all internal transactions in closed fashion, and make a finite Libra block chain for  interbank swaps. There is no need to maintain an infinite history, history is in the bounded market making risk accounts, everywhere bounded. Set up a trusted bank examiner system, use the existing credit systems to chase scofflaws. For merchants it is a much simpler system, faster system. Central bank volatility is gone, governments everywhere required to handle cash balances without fudging. Pure sandbox, add in FaceID,  a version of Secureid, competitive with Appleid. Bingo, done. Singularity time because micro payments value the link across any semantic network. Bearer digital cash becomes safe.

At this point the techniques are so widely spread the development time can be shortened by with fintech partnerships.  And as a side bonus, Zuck can force rationality into Congress.