You're acting as if Cyberpunk 2077 was made as an Nvidia tech demo, but something like DLSS is far too new for that. CD Projekt RED announced Cyberpunk 2077 back in 2012, while the first implementation of DLSS was released in 2019.
So, it's not very surprising that they would enter into a partnership with one or more GPU makers to push the limits. It would have been more surprising, in my humble opinion, if they had exclusively partnered with AMD.
There's a reason why Nvidia cards are selling and being used so much; it's not just marketing. Just take a look at, for example, the hardware survey on Steam, and see how many gamers are using Nvidia cards. Sure, fanboys can argue about Nvidia vs. AMD, but Steam clearly shows that Nvidia won that battle a long time ago, in every aspect.