AWS employee here. QLDB has been used internally at AWS for quite some time. We decided to turn our internal service into an external facing product because we saw a demand for a ledger system with central authority. Many people were trying to force Blockchain to accomplish this, while we already had an internal ledger solution that is far more scalable while still being cryptographically verifiable.
I think once centralized, there is inherently something wrong with blockchains. There is always chance of bait and switch, even though you trust amazon.
Sure but QLDB isn't a blockchain. Blockchain is just one of many things that can be implemented on top of it. You could implement the same thing with an SQL database and signed history tables.