They do mariculture corals in order to seed the reefs. I don't know about the Great Barrier Reef, but in Key Largo the Coral Restoration program does exactly this, but scaling up that kind of effort to replace what is lost is an incredible undertaking. Imagine trying to seed hundreds of square miles of dead coral reef.
https://www.coralrestoration.org/restoration
I've scuba dived several times off of key largo and have never seen acropora in the wild - the florida barrier reef lost most of its acropora due to pollution. The reefs there are sad in terms of coral diversity - lots of gorgonians, some zooanthids, but comparatively little living stony coral.