Nvidia also buys and licenses code from other companies. These days they’re on top of the chain, but they used to be a lot smaller. Maybe they rewrote their drivers to remove the external code, but I wouldn’t be surprised if they still have old external code in their drivers.
AMD tried to open their source code for a display technique (VRR I think? Not sure what it was) but was prevented from doing so by the standards authority, presumably because they used licensed reference code. I don’t think this applies to the older 10xx series of cards, but these factors are difficult to work around.