What's changed is that last year Tesla decided to publish an open standard. Now that other manufacturers can use the plug, they gave agreed to use Tesla's physical plug design, but with the CCS signaling protocol.
So NACS going forward is more of a new hybrid of the two rather than a switch to Tesla's existing charger. One of the outcomes is that cars equipped with CCS will be able to use NACS with a simple adapter.
Why not use Tesla's signaling protocol? I don't know the details. Maybe Tesla isn't ready or able to create an open standard for that part. Or maybe other manufacturers want to keep the signalling they have to keep adapters simple. In any case only one vehicle and charging station manufacturer (Tesla) will have to make updates on the software side, and to people who don't know the difference between the plug and the software it'll look like Tesla won the charger war.